Suppose someone wants to send you a large file. They could try to send it via email, but many email servers impose limits on file size. They could try sending it over during an instant messenger or Internet Relay Chat session, but that's slow, as the file actually gets transferred twice: once to the chat server, then to your machine. File transfer services like RapidShare and MegaUpload are fine, but not for confidential information. Of course, you could set up an FTP server on your box, but you don't want to leave that door open all the time. Luckily, there's now an easy solution: droopy.