Coolest software ever?

[TheCreator]

Question says it all- whats you coolest software you have ever made?
I don't mean something funny or entertaining but something that required real skill and is really useful.

[Kiana]

i wouldn't call this "useful" but to the extent of my narrow skill-set this is pretty impressive: i wrote a program that played an online computer game for you :)

[TheCreator]

thats actually really cool
what game? =)

[HenriK]

So you created a bot. Interesting...

[TheMassiveChipmunk]

I created a program that played Fur Elise by Beethoven on a virtual piano. This is not really useful either I just sucked at piano but I liked computers so in a way it is useful.