Lmms running on Ubuntu
LMMS is a free cross-platform alternative to commercial programs like FL Studio®, which allow you to produce music with your computer. This includes the creation of melodies and beats, the synthesis and mixing of sounds, and arranging of samples. You can have fun with your MIDI-keyboard and much more; all in a user-friendly and modern interface.
There are some sound demos that can be found here and screenshots can be found here. However, you can not make tracks where you record sounds. But you can use Audacity to fulfill that need. Both LMMS and Audacity works on Windows, Mac and Gnu/Linux but LMMS could need some extra tweaking to work with Mac os.