What are some good free music editing programs?

I’m looking for some solid programs, with the ability to add instrumentation like drums or bass if possible that are free and do not restrict the amount of time you can save of any particular music file. It must be able to handle multiple layers of music files so I could record things separately and combine them later. Any ideas?

I’m not interested in ‘free trial programs’ I need this to be a full program. :)