You can find a lot of beat maker software on the net. I think I should to test some and then determine which one is the best for you.
Consider these features of the software:
1: 16-track sequencer (not an 8-observe sequencer)
2: Individual volume control (for every of the sixteen tracks)
3: BPM Management (to control the tempo of the track)
4: Easy Export Possibility (a minimum of exportable to mp3 so you'll be able to burn the tune or upload it, etc.)