From Sirikata Wiki
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.
Try it out
You can try Sirikata out by downloading the current version and then visiting a Sirikata world. See the installation instructions for full details and then follow the scripting guide to learn how to script objects and build applications once you're in-world.
We love feedback. You can get in touch in a bunch of ways -- via email, IRC, or filing a bug. Any feedback, good or bad, is appreciated!
If you want to extend Sirikata's functionality (add a new scripting language, a different physics simulation, or better rendering), head to the platform development guide.
Looking for something in particular? Use the search in the top right or look through the list of all pages.