Where can I go to find open source high school level textbooks? I'm especially interested in geometry and algebra, though probability and trig are also useful.
I'm interested in rearranging and adapting these to my school's integrated math curriculum to fit the South African national curriculum.
This question is basically the same as Open-Source Math Textbooks, except I'm looking specifically for high school - not undergraduate - textbooks.
One example of what I'm looking for is Wikibooks but unfortunately most of these books are unfinished.