I know very few people who will find this interesting, but I'm one.
I'm teaching a little Algebra 2 this year, and I asserted to my students they'd never need to factor another quadratic equation if they implemented the quadratic formula within Microsoft Excel. For giggles, I decided to do it myself. It turned out to be more than a giggle's worth of effort.
I implemented it using 3 different formulas for each of the possible values of the discriminant (d>0, d=0, d<0 ). The work with the negative discriminant, of course, was the interesting stuff. IMPRODUCT, IMSUM, and IMPOWER were all new to me, and fun to see at work. It might make sense for me to reimplement the whole thing using IM functions, but I doubt I'll ever play with it again.
Anyway, Blogger doesn't allow me to upload arbitrary files like this (unless I name them .png or some such) so I can't post it out here. Drop me a comment if you want an ugly little notepad of an Excel spreadsheet that happens to be able to calculate any value for the quadratic formula.
Of course, if you're actually just interested in the roots of any given formula, you'll find Wolfram Alpha does ten times more than this little spreadsheet. The thought occurs to me to grow jealous and try to compete, but I'm not motivated enough.