From the Wikimedia Tech Blog:
We’re pleased to announce Beta Features, a way you can try out new features on Wikipedia and other Wikimedia sites before they are released for everyone.
Beta Features lets developers roll out new software in an environment where lots of users can use these features, then give feedback to help make them better.
Features Being Tested This Week:
Our first features are available now for early testing by logged-in users on MediaWiki.org, meta.wikimedia.org and on Wikimedia Commons.
How to Get Started
To test new features, check the items you want in the new Beta Features section of your user preferences and click ‘Save’ (see screenshot). You can also automatically enable all new beta features as they are released, if you like, and turn off any of these options anytime. To make it easier for you, a small ‘Beta’ link will show up next to ‘Preferences’ in your personal tools (the line at the top right of the page, or top left in right-to-left environments) when this extension is released worldwide in November.
Read the Complete Blog Post