On ubuntu you can install
$ sudo apt-get install lmms
It shows up as Application -> Sound and video-> Linux Multimedia Studio
When you launch it , you get the following screen.
LMMS offers the following features.
- Song-Editor for composing songs
- A Beat+Bassline-Editor for creating beats and basslines
- An easy-to-use Piano-Roll for editing patterns and melodies
- An FX mixer with 64 FX channels and arbitrary number of effects allow unlimited mixing possibilities
- Many powerful instrument and effect-plugins out of the box
- Full user-defined track-based automation and computer-controlled automation sources
- Compatible with many standards such as SoundFont2, VST(i), LADSPA, GUS Patches, and MIDI
- Import of MIDI and FLP (Fruityloops® Project) files
If you are looking for a good tutorial on LMMS see this video.