As someone who was in the demoscene: FastTracker II was more of a successor to ProTracker on the Amiga than it was a successor to ScreamTracker 3. I say this because I used it for years; if you go by user interface and keyboard shortcuts the heritage is very visible.

That isn't to say that FT2 didn't build upon what ST3 (ScreamTracker 3) did; FT2 loaded ST3 files and played them just fine, as long as they were sample-based and not OPL3 (basically no one used the OPL3 functionality in #trax); and a lot of the concepts were brought along as well; per-channel panning (not the hard LRRL of the Paula) and an option for a Linear frequency table (instead of using the Amiga's). I think ST3 had ADSR envelopes; FT2 definitely does.

There were other trackers about like MultiTracker, which got some use - it had a fairly interesting per-track compression (not just pattern compression) that was transparent to the user. It was the original format for Kenny Chou's (CC Catch) soundtrack to One Must Fall 2097 (which is public domain; if anyone can send me FALL1.MTM {"Powerplant"} I'd love you for days; I only have that one after I converted it to XM and it lost all the panning information, as FT2 does not store per-channel panning information; only per-instrument and per-sample; you can't just set a channel pan and have it persist)

No one was really using .MTM in 1995 onward tho.

ImpulseTracker was a 'proper' successor to ScreamTracker 3, down to how the interfaces looked and the keyboard shortcuts. Both are DOS Terminal / "ANSI" looking. ncurses was a thing back then but this was DOS; but they weren't using it. IT is still around and has been open-sourced and I think SchismTracker is the current flag-bearer fork - unsure.

FT2 vs IT was a hot topic in #trax in the late 90's; most of the cool kids used Impulse but I stuck to FT2.

ModPlug Tracker was the first really successful Windows tracker, it is and was FLOSS, and it's still around, and was a pretty capable tracker in its day if you didn't mind light mode. I think a lot of the more 'modern' module output plugins for GStreamer et al are based off of ModPlug code, but again I can't prove it (there was also the MikMod library/players; and CubicPlayer, etc. Tons of libraries)

MilkyTracker is the spiritual successor to FT2 (down to the keyboard shortcuts!) and runs on pretty much anything modern these days. I got it to run on the OLPC XO-1, which was plenty capable because modules were being mixed on a 486 or so at 33MHz, and the XO-1's Geode was running at 433MHz, which is a good 10x faster. However my biggest problem with tracking on the XO-1 was all the times I'd get interrupted when people would ask me about the computer I was working on...

iirc FT2 also had a "Disney Sound Source" parallel port option but never used it. It did have MIDI output.

FT2 did have a really shitty PC speaker output option, because almost all of them are shitty, and a really good one didn't happen until 8088mph came out. It was capable enough to annoy people around you, but it was also capable enough that a friend and I made some 4/6-channel XM files that used basically square wave samples that sounded decent enough. They're on modarchive, look for Comp Sci Chip Tech, you'll find them.