Animator is a project mainly written in JavaScript, it's free.
Tester for the animation mixin.
This is a SproutCore project that tests the performance of the animation mixin.
It works rather simply: the animation mixin has a lastFPS variable that holds the FPS for the last sequence of animations; this is an average from whenever the timer stops idling to when the timer starts idling again.
Our appController binds to that lastFPS property and updates the label in the toolbar. The results are much more consistent; I'm getting consistent results even with only 100 labels in super-fast Safari, with animations of only 5 seconds long (naturally, the longer the animation, the more consistent the data will be, as there will be more data collected).
The main_page.js will create a specified number of label views (one of the earlier lines in the file specifies it). Each label has a number so it can easily be tracked.