[girasquid]

There was at one point - Clutch (http://clutchio.github.io/) did it and then got acquired by Twitter. They've open sourced everything though (https://github.com/clutchio), maybe you can start researching from there.

[berzniz]

Clutch was great! I've used it myself, but you had to create the A/B tests while coding.

I'm going for a tool that lets you define the test after it was coded. Is that a big enough differentiator?