There are also some online ones, although I'm not sure how well they work in a multi-editor situation.
Might not be flexible enough for a really open brainstorming, but enough for stuff like figuring out domain concepts.
PlantUML - quick and simple text representation of diagrams, really easy to iterate on and see changes reflected live.
reveal.js - Quick and simple slide creation, I can reorder slides with ease, tweak wording, don't waste time faffing about with fonts, text box sizing etc. All reflected live in a browser.
This can be done by a script automatically executed at power-on, which may also choose how the buttons should behave, if you do not like the defaults.
For instance, for my Wacom stylus I set the tip to be left click, the first button to be right click and the second button to be double left click. Actually doing double click with the stylus buttons is more inconvenient, so it is more comfortable to map the single click on some button as a double click.
My kids even prefer that with a big (and pretty old) wacom tablet.
(P.S.: I apologize for other unanswered comments in the thread; I can't reply anymore because of how many days have passed since.)
I once got an bigger "upgrade" for my small wacom tablet, but it only collected dust. It used too much space on the desk to always keep it ready, and the larger active area meant too much travel distance when using the pen as a mouse.
And concerning Wacom, they were the first to have someone working on Linux drivers, and the only one for a long time, back when tablets were new. Not sure how it is today.
Wacom still has great Linux support, but now there's OpenTabletDriver which supports many other tablets [1].
In comparison with a mouse, a stylus is much more comfortable, much faster and more precise.
I'm using a "cheap" one (I think it was like 80 EUR), and it's mind blowing how convenient it is despite its small size. Now trying to use a physical whiteboard for brainstorming, feels the same way as trying to use pen and paper for programming: technically doable, but I curse internally because the inconvenience.
Just being able to select stuff and move it around, or undo with a quick Ctrl+Z, or rotate things, makes all the difference.
Sure, I love using a paper notebook for my notes, and the feel of writing with a pencil on paper is really nice; and I would use it for drawing quick stuff if I don't have anything else at hand. But if I think I'm going to be erasing a lot, or that I will be doing the kind of stuff that is usually done with a whiteboard, a drawing tablet is (to me) a vastly superior option.