When evaluating new platforms and frameworks it helps to know how active the developer community is and how much it's growing.
I've created a tool here that shows tag activity over the last 6 months at Stack Overflow:
Stack Overflow Size and Growth Tool
For example when comparing Javascript frameworks we can see that knockout.js has a bigger community, but angular.js is growing more quickly. angular.js has a bigger community and is growing more quickly than backbone.js.
The mass is the total number of posts and the momentum is a weighted average of growth over the last six months.
Mass and momentum are key factors to knowing which developer trends will turn into decisive shifts.