NetStylus transforms your Windows pen-enabled tablet into a drawing tablet for another device.
At the moment, I tested it only with my Microsoft Surface, and I wrote a server only for Linux (with libevdev). However, the "protocol" is straightforward and can be easily implemented also in other platforms.
The project is at a proof-of-concept level, but it does what it needs. I do not think I am going to add features/improve the ugly GUI soon.
If you want more information about how I wrote it, feel free to check this article on my website.