PS2, Gamecube, and Xbox games (and maybe a Wii game or two) that could have hypothetically appeared on the Dreamcast if the console had more time beyond 2001, primarily those published by Sega following the Dreamcast's discontinuation.

Also counting games that are known to have had Dreamcast ports planned but cancelled before release, and games that likely would have appeared based-on developer and publisher contributions on the Dreamcast. I'll also count enhanced ports of Dreamcast games that could have hypothetically been released as "special editions" of sorts on Dreamcast even if it is a bit of a stretch.