Some things that I use are:
Being able to write tab in a way that you can easily come back to it is such an important tool, being able to note down the exercises that you want to do or passages/songs for your own compositions to be able to come back to later for further development is invaluable. For my needs so far I've used Power Tab Editor. In no small way because it's free software but it's also fully functional so whilst there are paid options around there's no excuse for not getting your musical ideas down.
This is sadly paid software but for my part I wanted the ability to note down fretboard diagrams for my own preactice and development. It could be easily argued that there are other options out there when it comes to putting together fretboard diagrams but Neck Diagrams has everything that I wanted and more. The ability to tell it which scale you want over which part of the neck or in which position without having to manaully click each note is wonderful but there are many features that make this software an ease to use.