You can leave the TI graphing calculator at home thanks to this web-based TI-83 and TI-84 emulator. As with pretty much all emulators, this depends on a ROM image from the actual hardware to work.
The market is starting to hot up, though – and TI have recently been doing some interesting work with Python on their TI-83. Rumor has it that TI have been unable to get Python to run viably ...
Best I could ever do with my old TI-83 was make crude anatomical references.