Keychron, who make some of the best value mechanical keyboards and mice on the market, has taken the unusual step of providing source files for its hardware, providing fully editable files for elements like cases, plates and keycaps. Given that many of its best keyboards are already built on open-source VIA or QMK firmware, it's now possible to make quite radical alterations to your keyboard of choice.
The GitHub repository linked above makes clear that the hundreds of files being released aren't fully open-source - they're instead "source available". That means they can't be used as the basis for selling your own mechanical keyboard, for example, but Keychron's FAQ does encourage use of the files for personal or educational purposes. A company representative also clarified on GitHub that commercial use of the files to produce complementary accessories, such as replacement cases, is allowed.
As well as the files themselves, Keychron has provided guides on how to use them, how users can contribute to the project, links to their Discord server and other resources.
It's worth noting that the .step files provided here are detailed, editable designs rather than being simplified final products; they're analogous to a .psd file full of layers rather than a flattened, exported .jpg. That should make it a lot easier for users to 3D print or otherwise build their own complementary products, like replacement cases.
However, PCBs are not included in the release, so you'll have to create your own from scratch, adapt an off-the-shelf option - or modify an existing Keychron PCB.
Despite the limitations, it's a fascinating release that modders and enthusiasts will appreciate, and one that will hopefully prompt more companies to share their designs as commercial circumstances allow, especially older designs that aren't being actively sold.