Shake tracker is a MIDI sequencer aimed to all the tracker lovers who allways wanted to go midi, while keeping all sort of cool tracker features.
Shake tracker has a tracker-like interface which supports patterns, orders and IT-like effects.
Each track (midi channel) is subdivided in columns of it's on, so this adds an extra layer to pattern editing. Note on, Noteoff and velocity are also implemented the usual way, while the effect column understands most of IT commands with similar parameter ranges. Finally, there's also a controller/effects column and plans for adding "paintable controllers" support.
Shake tracker has been programmed with MIDI bandwith issues in mind, so it's perfectly usable on external synths, softsynths and soundcard synths. There is actually a Windows version of this program, but it's not native and it needs you to install an Xserver.
Many features of modern sequencers are still missing, such as sysex and midi in, but the program is perfectly usable and many people wrote songs with it (check downloads section).