GT.M[tm] is a vetted, industrial strength, transaction processing application platform consisting of a database engine optimized for high TP throughput and a compiler for the M (aka MUMPS) programming language. GT.M is open-souce freeware on x86/Linux.
GT.M V4.3-001B is now available. For the x86 GNU/Linux platform, this is mostly bug fixes. Details are in the release notes (available in the Docs section).
Source code is also available in CVS