What is LMMS?
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.
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
Source : http://lmms.sourceforge.net/