Open Hardware
lowRISC - A project to create fully open hardware systems. From the processor core to the development board, their goal is to create a completely open computing ecosystem.
Wikispeed - An open source automotive manufacturer that produces modular cars.
Open Source Ecology - A project to develop open source industrial machines, for building houses, farming, and more.


Video Games
Lakka - A linux distro preconfigured with retro video game emulators (from NES to PlayStation 1); supports controllers out of the box and has a user friendly interface similar to modern video game systems.


Free Art Software
Krita - A free and open source digital painting application designed for concept artists, illustrators, and texture artists. It actually has a decent interface, unlike gimp! xD!!!
GPLv2 licensed


List of websites that publish their own source
Neocities - Imagine geocities, except completely libre!

Img.bi - An image host that uses client side encryption to protect images from being snooped on by server admins.
GPLv3 licensed

Uguu.se - A temporary file hosting service based on the now defunct pomf.se.
MIT licensed

Hack.chat - A minimal, distraction-free chat application. Kind of like browser IRC, but with special features for discussing source code and LaTeX.
GPLv3 licensed

Sandstorm.io - A cloud hosting company for web applications. Designed to let individuals quickly deploy open source web applications without needing to worry about hosting or server configuration.
Apache 2.0 licensed

R/a/dio - An online radio station featuring anime music. Very cool website with a live-updating playlist.
MIT licensed


List of things that pretend to be open
Telegram - An instant messaging service. Their client software is licensed under the GPL to encourage developer adoption, but their server-side code is still proprietary.


See also:
Linux
Computers
Programming
Closed Source