For lyrics, I currently use Google Keep and hugely resent myself for it.
What I want is to be able to write lyrics as easily as plaintext, but with manually assignment of meter, rhythm etc, while also being able to "fork" lyrics at a point and be able to work on different threads, keep track of alternative lyrics on a phrase level too. Being able to sync that up with some basic music notation (e.g. keys and percussion) would get me 90% of the way to where I want to be when it comes to writing at the computer. I think I have a coherent design for such a software in my head but am unsure if it really is what I need or is just a whimsical distraction from not writing good enough lyrics yet. Would be interested to hear if anyone's seen anything like this (can't say I've exhaustively looked).