Schism Tracker is based off Impulse Tracker, and as such it isn't a ProTracker successor per se as the user interface is different.

It's absolutely a tracker, and absolutely part of the demoscene and quite a capable piece of software - but if you have the muscle memory for ProTracker (or FastTracker 2, as I do) keyboard shortcuts, it is not the same.

MilkyTracker does have an option for FT2-style shortcuts.