I wrote a song for Catie's recent birthday, using GarageBand, my keyboard, and a MIDI interface. Have a listen here: arr.m4a.
All the instruments are software instruments and were played on the keyboard (including the drums). The fairground theme was partially inspired by a (much better) song that Catie's friend Sarah once wrote for her named "Valse and Verhallend", but there are also elements of other tunes, such as the Millennial Fair theme from Chrono Trigger, and some things from Sky. It was fun to write, and by the end I felt that I had learnt something about how to put the next one together.