Futuristic sci-fi and cyberpunk graphical user interface framework for web apps. If you ever wanted to build a theme that looks like JARVIS or something out of Bladerunner, this seems like a good place to start.
Brutstrap is a CSS theme for building a brutalist website: one where the website, as shown in your browser, is an accurate representation of the HTML document it is displaying. Quite literally, the way the HTML is written is the way the page looks.
eDEX-UI is a fullscreen desktop application resembling a sci-fi computer interface, heavily inspired from DEX-UI and the TRON Legacy movie effects. It runs the shell of your choice in a real terminal, and displays live information about your system. It was made to be used on large touchscreens but will work nicely on a regular desktop computer or perhaps a tablet PC or one of those funky 360° laptops with touchscreens.
Themeable. Uses Electron. If Electron will run on it, it'll work.
Classic Shell is an open source application for Windows 8 that gives you a sane and usable desktop by replacing the Start Menu. It's skinnable, too, so you can make it look like Windows 7, Windows XP, or other versions of Windows.
OSclass is an open source clone of Craigslist that aims to be simple and easy to set up and administer. It is claimed that it has a management back-end that's even easier to work with than that of Wordpress. Written in PHP, uses MySQL. Themeable, has a plugin system.