Sega Technical Institute
From Sega Retro
The Sega Technical Institute was a very small group (basically 1-2 teams) that developed Sonic 2, Sonic 3, Sonic Spinball, and Sonic & Knuckles. It was originally staffed with Sonic Team members from Japan, then later with American folks. Also did some other games such as Comix Zone and The Ooze. STI's focus was to create character properties that could be built into a franchise.