Microsoft Delta is a short-lived commercial source control product, developed around an internal tool, called Source Library Manager (SLM, or 'slime' as it is commonly called). MS Delta was dropped off the shelves in lieu of SourceSafe, a product they acquired when they bought OneTreeSoftware? of North Carolina; however, that is the subject of a separate Wiki (and more pleasant memories).
The internal version of MS Delta, SLM, enjoyed a few more years of continued life, based on its ability to handle large software projects (larger than VSS could manage). It was replaced in 2000-2002 throughout most of the company by another internal SoftwareConfigurationManagement system called SourceDepot?. According to "Directions on Microsoft" magazine, Source Depot is a customization of a third-party product from Perforce.