As intelligent people in the business world, be it hedge funds, like Salman Khan, or computer programmers, begin to give back more and more free online tools are becoming available to teachers. Since these folks are intelligent, they actually work with teachers to design the interface that students and teachers or parents use.
Salman Khan speaks to an audience at a TED conference, some tech nerd conference with Bill Gates and the like.
You can sign up yourself to brush up on calculus and your students or children. I have started using the software ...Yes, it's free! and it's my favorite so far for the following reasons: 1) kids need instruction, not just practice; this is especially true if it just isn't making sense to them or if the student hasn't had instruction yet; 2) many practices, especially with math focus on speed and math facts, without encouraging kids to slow down and think; 3) there aren't enough resources for math beyond math facts; his videos teach calculus with practice activities. (I hope to be there in a few weeks after moving up each level before it!)
You can sign up or be a coach of a group, ideal for parents and teachers, by signing up at: http://www.khanacademy.org/
Enjoy. Maybe you'll try it to and fill in those gaps of mathematical understanding you may have.