Easy statistics for AdWords A/B testing, and hamsters
http://blog.asmartbear.com/easy-statistics-for-adwords-ab-testing-and-hamsters.html

Normally a formal statistical treatment would be too difficult, but I'm here to rescue you with a statistically sound yet incredibly simple formula that will tell you whether or not your A/B test results really are indicating a difference.

A simple javascript multivariate testing framework

Cohorts is a simple, purely javascript, multivariate testing framework. It allows you to easily run split tests for visitors on your site, showing them different designs, layouts, or whatever you want. Cohorts also allows you to track interesting events that occur for each of the cohorts. By default, it uses Google Analytics event tracking to store data, but you can customize it to use your own or another.