Makes me sad to say, but I've really tried a lot of different options to replace Garageband on Linux. I just have not found any good options thus far.
Why is Garageband good for me, a musician who plays instruments, and likes to create his own melodies, rhythm, percussion, strings, and other tracks?
It's dead simple to get started. I plug in my 88 Key USB Midi keyboard (detected automagically), create a new project, add a track, pick a sound (instrument) from a pre-installed list included with Garageband, and start playing / recording. Need another Track, add a track, pick a sound, start playing / recording. Need to switch back, just click the track and done.
Thus far on Linux my experience has not been so smooth. I tried LMMS (which is okay, but getting sounds is not simple or straight-forward. Recording, still haven't figured out how to record a track. Want to hear the sound on track 2, oh wait, you have to go tell the midi connection that you no longer want track 1, and now want track 2. Rosegarden...nice, but first I had to spend weeks trying to understand JackCTL, then find a synth to connect it to, then figure out why my midi keyboard wasn't detected, then once I could play a sound, forget about switching tracks...OMG!
And thus far, pretty much everything I've tried has had some level of similar complication. Ardour, QTractor, Reaper, Waveform Free from Tracktion, and on, and on.
I love open source software, but it has got to be easier for the average bear. I just want to connect up, sit down, and start playing / recording. I just want to switch tracks, and the system knows...ohhhh you want to record strings now...not brass...ok. If anyone has something that will work with anywhere near the ease of Garageband, but on Linux, please let me know about it.