Tarantool is an in-memory database and application server.

Key features of the application server:
- 100% compatible drop-in replacement for Lua 5.1, based on LuaJIT 2.1. Simply
  use #!/usr/bin/tarantool instead of #!/usr/bin/lua in your script.
- full support for Lua modules and a rich set of own modules, including
  cooperative multitasking, non-blocking I/O, access to external databases, etc

Key features of the database:
- MsgPack data format and MsgPack based client-server protocol
- two data engines: 100% in-memory with optional persistence and a 2-level
  disk-based B-tree, to use with large data sets
- multiple index types: HASH, TREE, RTREE, BITSET
- asynchronous master-master replication
- authentication and access control
- the database is just a C extension to the app server and can be turned off

WWW: https://tarantool.io/