TikZ (a self-referential acronym for Tikz Ist Kein Zeichenprogramm) is an excellent, and extremely versatile drawing program. I highly recommend it.
There's an extensive manual. It might be frightening at first sight, but it in fact starts very gently, with a long list of worked examples (starting on page 30).
There's also some humorous examples of things not to do when designing a graphic (check out the stuff around page 99).
