Who needs Texas Instruments? Not Matt Stack, creator of the Open SciCal. His homemade, 100% open source graphing calculator not only blows away the functionality of store-bought devices, but is the "ultimate status symbol among the nerdiest of the nerds."
When I was in high school, stolen TI-83s were a pervasive trade, the scourge of the number-crunching and SAT-prepping. I can only imagine what sort of criminal enterprise would have sprung up had kids been walking around with Stack's fully customizable wonder-calc, boasting a touchscreen, 1-GHz ARM Cortex A8 processor, 8GB of SD storage, and Wi-Fi.
So just what exactly can you calculate with that whopping ARM processor? Pretty much anything you want. Stack demonstrated the flexibility of the Open SciCal by inputting data on sunspots to get a statistical prediction on the next solar blast, and crunched financial trends with with stock quotes from Yahoo. Pulling off your own quantitative project shouldn't be tough, as the calculator runs Linux and R, and can program in Perl and C.
To be fair, the Open SciCal does cost about $200 to assemble—far more than any basic graphing calculator. But for the price, Stack maintains his calculator offers double the functionality of anything you can buy off the shelf, plus the ability to modify as much as one pleases.