Drizzle is a micro-kernel designed database system. Its relational and durability goals are built into the kernel as a default design. It supports a number of interfaces which are "pluggable" so that the kernel does as little as possible, and is as clear as possible to users. This allows users to extend the database by writing simple plugins.
Drizzle supports SQL92, with custom extensions for advanced users.
Historically, database servers have dictated infrastructure - you must use the inbuilt authentication system, the inbuilt logging system etc. Drizzle takes a different approach; it aims to integrate with your existing infrastructure, becoming a part of it instead of an island.
Drizzle has been designed for modern environments, which are 64bit, multi-core with gigabytes of memory.
Drizzle is open source software, and is maintained by a number of individuals and companies for the better advancement of all who participate.