LMMS

Very easy to use and pretty powerful MIDI creator!!!

One of the rare audio applications actually works with PulseAudio on Ubuntu 20.04 out-of-the-box, so you don't have to turn off every other audio application!!!

Has lot's of plugins built-in just working out of the box, e.g. ZynAddSubFX out-of-the-box without doing a gazillion complex setup connections.

Most plugins are just simple toys however, ZynAddSubFX is the only super powerful one. The others are more LMMS integrate however, and seem to use a more dedicated LMMS GUI style.

TODO can you do liver performance with a virtual instrument?

If you open vmpk, you can then right click on a piano track, and go MIDI, Input and it just shows up there, and it does produce sound as shown at: www.youtube.com/watch?v=NpeP2th08ak

TODO: what about recording the input MIDI? Yes, there is a record button on the piano roll!