I am wondering if there is anything similar to ink over apps for linux. i.e. , a program that allows me to draw over any other program given Xs architecture, it should be possible, but I looked for it and could not find it.
EDIT: I have two good suggestions by Roman Raguet: one in his answer, and one in the comments.
I'd like more suggestions, and, if possible, one that does not require a composite window manager