It exist many programs for Linux , you can find a list in different Categories on these 2 really nice Sites

http://www.linuxaudio.org/members

http://www.linux-sound.org/

http://www.renoise.com/

Renoise has a unique bottom-up approach to music making. With its vertical timeline and streamlined interface, Renoise lets you have direct control over the composition. 

Its a really cool program i often use it, but its not FREE (for testing theres a Demo Version). Its made for Linux, Windows & Mac and if you want to buy it its not expensive and i think you´ll should support the programm!

http://lmms.sourceforge.net/

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.

 Ardour is a digital audio workstation. You can use it to record, edit and mix multi-track audio. You can produce your own CDs, mix video soundtracks, or just experiment with new ideas about music and sound. 

 Audacity® is free, open source software for recording and editing sounds. It is available for Mac OS X, Microsoft Windows, GNU/Linux, and other operating systems