Minecraft Enchantment Calculator is an open source website for calculating the probability of getting a chosen enchant in Minecraft.
The site is live here. Feel free to hack around with the source, it's a bit of a mess right now but I will get around to cleaning it up soon. I make sure to read all pull requests and issues, but due to work and school I am usually unable to get things fixed immediately.
The calculator is written using jQuery, and uses the algorithm described here on the Minecraft Wiki.
I no longer accept donations for this project, however there is an official iOS app for the calculator here if you're feeling generous!