Currently in open beta, you can get an invite by visiting http://atom.io/
and entering your e-mail address.
Atm it's Mac only, Linux & Windows will follow.
It looks quite similar to Sublime Text and has already a large range of supporting plugins.
The core is closed source atm. Although it's not obfuscated
The repository for plugins: https://github.com/atom
Multiple cursors are already supported and an experimental vim plugin is available.
Screenshots are available on the website and most of the plugins in the repository have one / several as well...
A video that shows some of it's features: