Ever been stuck doing a maths assignment in the middle of the night, and trying to work out how to goddamn differentiate a silly equation like sin(x)*x when all your mates are asleep? Or how about being about to chuck your computer out the window because MATLAB is being an absolute pain in the arse and you can't solve the equation?
Been there, done that. And now here's how do that the easy way. Calc5.
What?
Check out
http://www.calc5.com.
It's a graphical scientific & symbolic web-based calculator. You'll have to learn a couple of commands here and there to do graphs and differentiation etc. but it looks a helluva lot better than MATLAB, works fast, doesn't take ages to load, and doesn't require you to feel guilty for cracking MATLAB so you don't have to spend what little non-uni time you have left at uni.
It does symbolic maths as well (as does MATLAB with the help of the Symbolic Maths Toolbox, which is effectively MAPLE, however many people don't seem to realise this), so you can tell it to differentiate sin(x)*x and it'll give you the answer with the variables still in it (e.g. x*cos (x)+sin (x)).
Of course, its not a complete replacement, and is a work in progress (e.g. doesn't support numeric/symbolic integration yet), but its something I'd definitely be using for those annoying small calculations that you just can't work out (or when your assignment is due in 3 hours and you haven't started).