What is Sirikata?
Sirikata is a BSD-licensed platform for virtual worlds. Instead of a single world, Sirikata lets anyone create a custom virtual world. All the common, core components of virtual worlds are built-in -- servers that simulate the world and distribute content, a graphical client, and scripting language support — allowing you to focus on creating the objects and behaviors unique to your world.
You can try Sirikata out by downloading the current version and then visiting a Sirikata world. The user starting page has complete instructions, and once you're connected, you'll also find information about getting started with scripting objects and building applications in-world.
If you want to extend Sirikata's functionality (add a new scripting language, a different physics simulation, or better rendering), head to the platform developer's starting page.
The Getting Started pages have links for different mailing lists, IRC, and other modes of communication specific to the type of question or request. You can also mail the general mailing list.
Looking for something in particular? Use the search in the top right or look through the list of all pages.