In the summer of 2021, I did a stupid thing, and bought a SL-100/CS-2100 telephone switch. See more of the story here.
The SL-100, also known as the MSL-100 (Meridian SL-100), shares a common hardware platform with the DMS-100 and the entire DMS line of telephone switches. The SL-100 is effectively the PBX version of the DMS-100. In addition, the CS-2000 was developed as a VoIP telephone switch to accompany the DMS-100. The two seem to be able to coexist as if they were a 'single' switch, and are joined by special hardware in a DMS SPM (normally used for OC-3 connections). The CS-2100 is simply the PBX version of the CS-2000, to accompany the SL-100.