Aria Maestosa is an open-source (GPL) midi tracker/editor. It lets you compose, edit and play midi files with a few clicks in a user-friendly interface offering keyboard, guitar, drum and controller views.

Features:

Import and play MIDI files

Easily compose and edit music

See and use musical score notation, as well as piano roll, tablature and/or drum views

Print musical notation (only in version 1.2+)

Record from a MIDI instrument (only in version 1.3+)