What are some good 5e companion apps?

What apps do all of you use, aside from pencil and paper?

I've been trying to find a good digital app to keep track of my character and item, but I'm not rebuying all my books on beyond, I have physical copies of all of them.

Also looking if there are any good spellbook apps. Currently I use one just called spellbook that keeps a list of favorites, prepared and known.