Richard McMahon has written about using Perforce as the SCM with SwitchTower (here). He’s even written a custom Perforce SCM module for SwitchTower, so if you’re a Perforce user wanting to dabble with SwitchTower, it looks like you’re in luck.

(Richard has given his permission for the Perforce SCM module to be included with the next SwitchTower release.)