The Linux kernel has been ported to the Texas Instruments TI-Nspire. The TI-Nspire series platform powers higher-end graphing calculators in recent years from the Dallas-based company.
Texas Instruments' Nspire platform is used by their Clickpad, Touchpad, CX, and CM-C graphing calculators. The TI Clickpad launched in 2007 while the other Nspire models are from more recent years.
The TI-Nspire is powered by an LSI ARM926EJ-S with speeds up to 200MHz, 32MB of SDRAM (or 64MB for the newer CX model), NAND flash, 320x240 display, and a USB controller.
The Nspire calculators run a proprietary Nuclear-based OS and Texas Instruments has fought before from developers putting native code on the hardware. In fact, the only official methods for programming on the TI-Nspire is through a restricted BASIC implementation or a proprietary Lua that isn't compatible with upstream Lua. Now, there's a Linux kernel port to this calculator hardware.
This Linux kernel port was done by Daniel Tang and not officially sanctioned by Texas Instruments. The TI-Nspire kernel patch allows for booting Linux to a shell on all of the claculator models but doesn't support much more than that at the moment. Most of this TI-Nspire Linux support was done through reverse engineering the platform.
At the moment this Linux kernel port is less than 2,000 lines of fresh code to mainline. The patch and more details on the TI graphing calculator port can be found on the kernel mailing list