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Back in my day, calculators were used for complex equations, double-checking mental arithmetic and giggling over an upside down screen reading 5138008. These days, it seems the updated abacus is capable of a little more than that, with one gamer cleverly programming a version of Portal, which runs exclusively on Texas Instruments calculators.
There are 38 testing chambers (and a level editor!), but can only be played on the Ti-83 and Ti-84 series calculators. Sure, it's not the original game, but it does twist space and time in the same sort of ways. Portal Prelude is set inside Aperture Laboratories"long before GLaDOS ever ran the facility."
...now, if you don't have the right hardware, we hear that there are calculator emulators available for the PC (no, really), but doesn't that defeat the purpose just a little?
Jimmy the Geek