There are many alternatives to Microsoft SQL Server for Windows if you are looking for a replacement. The best free Windows alternative is SQLite, which is also Open Source. If that doesn't suit you, our users have ranked more than 50 alternatives to Microsoft SQL Server and many of them are free and available for Windows so hopefully you can find a suitable replacement. Other interesting free Windows alternatives to Microsoft SQL Server are PostgreSQL, MySQL Community Edition, MariaDB and MongoDB.
SQLite is a software library that implements a self-contained, serverless, zero-configuration, transactional SQL database engine. SQLite is the most widely deployed SQL database engine in the world. The source code for SQLite is in the public domain.
PostgreSQL is a powerful, open source object-relational database system with over 35 years of active development that has earned it a strong reputation for reliability, feature robustness, and performance.
MySQL Community Edition is a freely downloadable version of the world's most popular open source database that is supported by an active community of open source developers and enthusiasts.
MariaDB is a backward compatible, drop-in replacement of the MySQL® Database Server. It includes all major open source storage engines.
MongoDB is a document database with the scalability and flexibility that you want with the querying and indexing that you need
DbGate is cross-platform database manager. Simple and effective, allowing to work with many various databases simultaneously - SQL and NoSQL.
Apache CouchDB is a distributed, fault-tolerant and schema-free document-oriented database accessible via a RESTful HTTP / JSON API. It includes incremental map / reduce mechanics for queries and keeps data safe with an append-only datastore.
The Apache Cassandra database is the right choice when you need scalability and high availability without compromising performance.
DB2 offers industry leading performance, scale, and reliability on your choice of platform from Linux to z/OS. DB2 supports storing XML and relational data and offers SQL PL and PL/SQL procedural languages.
Firebird is a relational database offering many ANSI SQL-92 features that runs on Linux, Windows, and a variety of Unix platforms. Firebird offers excellent concurrency, high performance, and powerful language support for stored procedures and triggers.
Datomic is a database of flexible, time-based facts, supporting queries and joins, with elastic scalability, and ACID transactions.
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Its free with same power of MS SQL