I've used Smooze [1] in the past. It has a ton of features, but I really just need it for turning off mouse acceleration and making the scroll wheel usable. Glad to see an open source option.
I'm using https://github.com/ther0n/UnnaturalScrollWheels, literally the only thing it does is invert the scroll wheel direction.
"You're holding it wrong" taken to absolute mastery.