All our own, and many commissioned, designs are created under the Creative Commons Attribution-NonCommercial 3.0 license. This allows you to take our board designs and expand upon them. All we ask in return is a nod in our direction as the original designers.
Not only is the majority of the software we write open-source (released under the BSD 3-clause license) but in-house we only use open-source software. That includes all our EDA tools, such as the gEDA suite.
One of the biggest movements in the open-source hardware field is Arduino environment. We are heavily involved with a sister system, chipKIT, which aims to bring the power of Microchip's PIC32 microcontrollers to Arduino. As part of that we are constantly writing and improving libraries to support both the PIC32 chips and their peripherals, but also for supporting third party hardware connected to chipKIT boards. All our libraries are open-source and published on Github.
By far the biggest library (rather a suite of libraries) we have created is the DisplayCore system for chipKIT. This is a professional grade object-oriented graphics programming environment for TFT and other displays attached to chipKIT boards. Boasting over 70 fonts and a fully event-driven GUI system DisplayCore allows you to easily and rapidly create professional and functional user interfaces for your projects.
Read more on the DisplayCore website: DisplayCore.org