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.
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+)