SymmetricDS is a database and file synchronization solution that is platform-independent, web-enabled, and database agnostic. SymmetricDS was built to make data replication across two to tens of thousands of databases and file systems fast, easy and resilient. It supports near real time, bi-directional data replication across large node networks over the WAN or LAN.

SymmetricDS - Multi Database Replication

SQL Relay is a persistent database connection pooling, proxying and load balancing system for Unix and Linux supporting ODBC, and all major databases. It has APIs for C, C++, ODBC, Perl, Perl-DBI, Python, Python-DB, Zope, PHP, Ruby, Ruby-DBI, Java, TCL and Erlang, drop-in replacement libraries for MySQL and PostgreSQL clients. 
 The APIs support advanced database operations such as bind variables, multi-row fetches, client-side result set caching and suspended transactions. It is ideal for speeding up database-driven web-based applications, accessing databases from unsupported platforms, migrating between databases, distributing access to replicated databases and throttling database access.

SQL Relay is a persistent database connection pooling, proxying and load balancing system for Unix and Linux supporting ODBC, and all major databases. It has APIs for C, C++, ODBC, Perl, Perl-DBI, Python, Python-DB, Zope, PHP, Ruby, Ruby-DBI, Java, TCL and Erlang, drop-in replacement libraries for MySQL and PostgreSQL clients.

SQL Relay - Database Connection Pool library with API available in all programming languages

Perst is McObject's open source, dual license, object-oriented embedded database system (ODBMS). Perst gives developers the ability to sort, store and retrieve objects in their applications with maximum speed and with low memory and storage overhead, while leveraging the object-oriented paradigm of Java and C#. It is available in one edition developed as an all-Java embedded database, and another implemented in C# (for Microsoft .NET Framework applications). Perst’s also include garbage collection, schema evolution, a “wrapper” that provides a SQL-like database interface (SubSQL), XML import/export, database replication, support for large databases, and more.

Perst is McObject's open source, dual license, object-oriented embedded database system (ODBMS). Perst gives developers the ability to sort, store and retrieve objects in their applications with maximum speed and with low memory and storage overhead, while leveraging the object-oriented paradigm of Java and C#. It is available in one edition developed as an all-Java embedded database, and another implemented in C# (for Microsoft .NET Framework applications).

Perst - object-oriented embedded database

BookKeeper is a replicated log service which can be used to build replicated state machines. A log contains a sequence of events which can be applied to a state machine. BookKeeper guarantees that each replica state machine will see all the same entries, in the same order. It provides back end support to distributed systems, such as messaging systems, coordination systems, filesystems, etc.

BookKeeper - Replicated Log Service

Tendermint Core is Byzantine Fault Tolerant (BFT) middleware that takes a state transition machine - written in any programming language - and securely replicates it on many machines.
 
Tendermint is software for securely and consistently replicating an application on many machines. By securely, we mean that Tendermint works even if up to 1/3 of machines fail in arbitrary ways. By consistently, we mean that every non-faulty machine sees the same transaction log and computes the same state. Secure and consistent replication is a fundamental problem in distributed systems; it plays a critical role in the fault tolerance of a broad range of applications, from currencies, to elections, to infrastructure orchestration, and beyond.
 
Tendermint consists of two chief technical components: a blockchain consensus engine and a generic application interface. The consensus engine, called Tendermint Core, ensures that the same transactions are recorded on every machine in the same order. The application interface, called the Application BlockChain Interface (ABCI), enables the transactions to be processed in any programming language. Unlike other blockchain and consensus solutions, which come pre-packaged with built in state machines (like a fancy key-value store, or a quirky scripting language), developers can use Tendermint for BFT state machine replication of applications written in whatever programming language and development environment is right for them.

Tendermint Core is Byzantine Fault Tolerant (BFT) middleware that takes a state transition machine - written in any programming language - and securely replicates it on many machines.

Tendermint - Tendermint Core (BFT Consensus) in Go

Tungsten Replicator is a high performance, data replication engine for MySQL. It offers a set of features like Global transaction IDs to support failover, Flexible transaction filtering, Extensible transaction metadata, Sharding, Multiple replication services per process and lot more. Tungsten Replicator prompts masters easily from pools of slaves, Replicates data between different database versions, Replicating efficiently across sites, Building complex topologies, and Parallelizing data flow between servers. Tungsten Replicator runs equally well in cloud as well as locally hosted environments.

Tungsten Replicator is a high performance, data replication engine for MySQL. It offers a set of features like Global transaction IDs to support failover, Flexible transaction filtering, Extensible transaction metadata, Sharding, Multiple replication services per process and lot more.

Tungsten Replicator - Data Replication Engine for MySQL

Slony-I is a "master to multiple slaves" replication system with cascading and failover. Slony-I is a system designed for use at data centers and backup sites, where the normal mode of operation is that all nodes are available. 

Slony-I - Replication System for PostgreSQL

Galera cluster provides distributed, multi master support for MySQL and MariaDB. Its feature include Synchronous Replication, True Multi-master, Active-Active Cluster Read and write to any node at any time, Automatic Node Provisioning, Multi-threaded Slave and lot more. 
 
Galera Cluster is a superb replication system when using MySQL or MariaDB for your databases. However, it does have some limits for which you may want to be aware before migrating to it. Within the database server, other than the system tables, which use MyISAM, only InnoDB tables are allowed. InnoDB is used because it’s an excellent transactional storage engine. All tables must have an explicit primary key, either a single or a multi-column index.

Galera cluster provides distributed, multi master support for MySQL and MariaDB. Its feature include Synchronous Replication, True Multi-master,  Active-Active Cluster Read and write to any node at any time, Automatic Node Provisioning, Multi-threaded Slave and lot more. 

Galera - Cluster for MySQL and MariaDB

LizardFS Software Defined Storage is a distributed, parallel, scalable, fault-tolerant, Geo-Redundant and highly available file system. It spreads data over a number of physical servers, making it visible to an end user as a single file system. 
Data is distributed among multiple chunk servers. You can easily add and remove drives or the whole storage nodes. It is as simple as “plug and scale”. You can easily scale your LizardFS cluster up and down both vertically and horizontally by a single drive or a single node. You can have thousands of chunkservers and up to 1 Exabyte of data. Geo replication allows you to create geo stretched clusters stretching virtually any distance.

LizardFS Software Defined Storage is a distributed, parallel, scalable, fault-tolerant, Geo-Redundant and highly available file system. It spreads data over a number of physical servers, making it visible to an end user as a single file system.

LizardFS - Software Defined Storage, Distributed, Parallel, Scalable, Fault-tolerant, Geo-Redundant and Highly available file system

Bucardo is an asynchronous PostgreSQL replication system, allowing for both multi-master and multi-slave operations. 

Bucardo - Asynchronous PostgreSQL Replication System

DBBalancer is some sort of middleware that would sit in between of database clients  and a server. Currently the only server supported is Postgres, but the architecture is open to embrace more servers in a future. It's a connection pool, a load balancer and a database replicator. 

DBBalancer - Middleware btw Database client and server

db4o open source object database, native to Java and .NET. Its power comes from allowing arbitrarily complex, application defined, class models to also represent your database schema. 
	
 <UL>
	<LI>Support for Mobile</LI> 
	<LI>First embedded DB to support LINQ</LI>
	<LI>Full support for Compact Framework plus Sync capabilities</LI>
	<LI>Compatible with ADO.NET DataServices API</LI>
	<LI>Object persistence out-of-the-box</LI> 
	<LI>Free Object Manager plugin for DB exploration (OME)</LI> 
	<LI>No schema mapping complexity</LI>
	<LI>Zero Administration</LI>
	<LI>Replication</LI>
	<LI>Embeddable</LI>
	<LI>Native Queries</LI>
 </UL>

db4o open source object database, native to Java and .NET.

db4o

Copycat is a fault-tolerant state machine replication framework. Built on the Raft consensus algorithm, it handles replication and persistence and enforces strict ordering of inputs and outputs, allowing developers to focus on single-threaded application logic. Its event-driven model allows for efficient client communication with replicated state machines, from simple key-value stores to wait-free locks and leader elections. You supply the state machine and Copycat takes care of the rest, making it easy to build robust, safe distributed systems.


Copycat - A novel implementation of the Raft consensus algorithm

DBTransfer is a multi-platform java tool, that aims to replicate one database (JDBC or MS Access) to another (JDBC), using an one to one conversion. 
Its features include: 
<ul>
<li>Copy data from one database type to another type. Example: you can
migrate your MSSQL to PostgreSQL, without losing the structure,
including not only the original schema, the constraints, and of course,
the data it self, which is converted to respective data-type.</li>
<li>Copy one database schema to another.</li>
<li>Move data from one database to another.</li>
<li>Compare two databases.</li>
</ul>

DBTransfer is a multi-platform java tool, that aims to replicate one database (JDBC or MS Access) to another (JDBC), using an one to one conversion.

DBTransfer - Versatile and fast database transfer tool

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