Mobile performance testing platform from akamai based on the webpagetest.org infrastructure, free. Useful.
A good introduction to the statistics math of split testing.
Includes the math behind the calculation, and sample PHP code to actually generate the numbers. Very cool.
Simple formula to calculate statistical significance at 95% on AB / split tests. N = total clicks, D = diff between win & lose, if D² > N, it's statistically significant. Example, 14 clicks A, 22 clicks B, N=36, D=22-14=8, 8²=64>36, win. If 2D²>N, 99%.