I google midi trackers yeasterday.
There are few commercial and one for unix...

Also there is excellent one by SIDwizard author (Hermit).
Its opensource and looks very nice!

LINK:
https://sourceforge.net/projects/miditrk/

SCREENSHOT:

And keyboard layout is very similar to SIDwizard so thats fine!

So enjoy!

Hmm, this looks interesting. Will have to try building on RPi, could be awesome.
Yogi