MariaDB is a database server that offers drop-in replacement functionality for MySQL. It is built by some of the original authors of MySQL, with assistance from the broader community. In addition to the core functionality of MySQL, it offers a rich set of feature enhancements including alternate storage engines, server optimizations, and patches.
HailDB is a relational database in shared library form that can be embedded into applications. It is not a SQL database, although you can use this library as the storage backend for a SQL database. It features a clean and simple API and is a continuation of the Embedded InnoDB project. With the addition of the HailDB plugin to Drizzle, you get a full SQL interface.
Infobright Community Edition (ICE) is an analytic database built on MySQL, designed to deliver very fast query response against large data volumes. It is a self-tuning, columnar database that eliminates the need to create or maintain indexes, partition data, or perform other administrative tasks.
deltasql is a tool to synchronize databases with source code, which helps to keep database evolution under control. While developing mid-sized or big applications, developers make changes to the data model that go along with changes to the source code. From time to time, branches of source code are done to stabilize the code that will go to production. A sort of data model branch is also needed. deltasql provides a simple way to collect all scripts that change the data model and means to handle data model branches. The deltasql server runs on Apache and is backed by MySQL.