What is your most-used web application? Fairly straightforward question. It shouldn't be too hard to guess what will come out on top, but I'm interested to see what else gets high votes.
ONE entry per post and NO duplicates.
The following applications have already been listed.
Use the following search query
inquestion:2050 "example name"
Why do you use this one more than anything else and what does it actually do? Should I use it too?