Gromix-MPX is a basic but handy annotation tool. The best thing about the program is its ability to toggle on/off functionality which lets you draw on-screen, then disable drawing, and then re-enable drawing on-screen again when needed.
There’s lots of features that would improve the tool such as the ability to draw straight lines, the ability to draw pre-defined shapes and arrows, as well as the ability to change the pen color on the fly.
Gromix-MPX is free and open source software.
Developer: Christian Beier (author of the original Gromit annotation tool is Simon Budig)
License: GNU General Public License v2.0