GT.M is a high-throughput key-value database engine optimized for transaction processing. (It is a type also referred to as "schema-less", "schema-free," or "NoSQL.") GT.M is also an application development platform and a compiler for the ISO standard M language, also known as MUMPS.GT.M, an abbreviation for Greystone Technology M, was developed by the Greystone Technology Corp in the 1980s. It is an implementation of ANSI standard M for several UNIX systems and Linux.