Tarantool is a NoSQL database management system running in a Lua application server. The code is available for free under the terms of BSD license. Supported platforms are GNU/Linux, Mac OS and FreeBSD. Key features Unlike most of NoSQL databases, Tarantool supports primary, secondary keys, multi-part keys, HASH, TREE and BITSET index types. Tarantool supports Lua stored procedures, which can access and modify data atomically. Procedures can be created, modified and dropped at runtime. Use of Lua as an extension language does not end with stored procedures: Lua programs can be used during startup, to define triggers and background tasks, interact with networked peers. Unlike popular application development frameworks implemented around “reactor” pattern, networking in server-side Lua is sequential, yet very efficient, as is built on top of the cooperating multitasking environment used by the server itself. Extended with Lua, Tarantool typically replaces more not one but a few existing components with a single well-performing system, changing and simplifying complex multi-tier Web application architectures. Tarantool supports replication. Replicas may run locally or on a remote host. Tarantool replication is asynchronous and does not block writes to the master. When or if the master becomes unavailable, the replica can be switched to assume the role of the master without server restart.