Mac (Windows/Linux coming soon): Atom, the text editor from the folks at GitHub and one of your favourites, is now open source and free to download and use. The team is still working on Windows and Linux versions, but the Mac version is out of closed beta and available to all.
Atom is still in beta, and it's not truly feature-complete just yet, but it has created a lot of developer buzz. It's themable, so you can customise the look and feel. It's also modular, so you can add specific packages that support the type of development work you're doing. It has an open, developer-friendly API, so third party devs can contribute to it if they want. It features a tabbed interface, multi-paned layout, easy file browser, and easy learning curve so you can get up and running with it quickly.
The GitHub team explained that they're still working on the tool, but part of the move is to encourage the community to build and start hacking with it. If you're using OS X, you can download Atom right now and give it a whirl at the link below. It's free, and available under an MIT licence.