One nice thing about Casio is that, unlike TI, they aren't actively cracking down on the modding scene for their calculators. There's no official SDK, either, but the community has successfully made a gcc-based one themselves, and reverse-engineered and documented much of the OS APIs. Consequently, it is possible to write apps for it that have all the same abilities as native ones, and sideloading is trivial - you just mount the calculator as a USB Mass Storage device and copy the binary over. NESizm is probably the most impressive community-made app so far, but other goodness includes a port of Lua, and even a multiplayer 3D game (<a href="https://www.cemetech.net/downloads/files/2319/x2749" rel="nofollow">https://www.cemetech.net/downloads/files/2319/x2749</a>).<p>In theory, it is possible to replace the entire OS, and some people have tried rolling their own from scratch, but I don't recall any of those projects getting past the prototype stage. I do wonder if some kind of basic Unix-like is possible given the hardware constraints - 58 MHz CPU and 2 MiB RAM is not much, but there were historical Unix machines with far less. However, if one were to do a port rather than writing it from scratch, what would be the best thing to base it on? Minix?<p>For the curious, here's the community wiki that documents the platform:
<a href="https://prizm.cemetech.net/Prizm_Programming_Portal/" rel="nofollow">https://prizm.cemetech.net/Prizm_Programming_Portal/</a>