A lot of people don't realize this, but the concept of tool-assisted speedrunning had actually started from the Doom community. However, the TAS'ing capabilities for that game are relatively primitive. While console emulators have all those fancy features, the TAS-enabled Doom ports (e.g., TasDoom, MBF and PrBoom) offer only basic ones, such as save states, rerecording and slowdown. I'd love to see more TAS features added to those source ports.
There's a more advanced port called DooM Replay Editor that supports Frame Advance, displays player speed/coordinates, etc. The savestate code isn't perfect, but the whole thing is perfectly stable and reliable if you follow a few simple rules that no one's ever bothered to write down.:-) I've created several demos with it and, in all my usage, have only run into one desync.