DSM went to InterSystems Corp. during their spree of buying up every MUMPS implementation vendor they could get their hands on. They got DataTree (DTM), Micronetics (MSM), and DSM. They already had ISM. They merged ISM and features from the others into OpenM, which evolved into Caché, their current MUMPS product.
M21, GT.M, MUMPSv1, FreeM, YottaDB, and Mumps-II remain independent and current as of today. I'm the station chair for the validation and testing suite for the MUMPS Development Committee, which is the organization responsible for the ISO and formerly ANSI standards for the language.
