What tools do you use for design documents?

I am looking into wheter or not it is beneficial to write design docs for personal projects. I have decided to try it.

There is enough info on what design doc should contain, but very litle on how they are actually made. I am particulary interested on programs used to create, distribute (to other devs) and maintain design docs. For example I would like to use msword with the projects github repo, but unortunately I couldn't see the file straigth from browser.

Mostly I am looking into free solutions, but feel free to also add paid services if they realy are good for thia kind of stuff.

My intuition days that it would be best if these questions are answered: 1. Software for writing docs 2. What to use for distributing docs 3. What kind of group is this good for (solo project/other small project/big project, etc.)

Thanks in advance!