AirDroid is a free web-based interface to your phone that allows you to manage tons of tasks from your computer that you normally would have to delve deep into your HTC EVO to do.
On my EVOs, when I want to copy some pictures I usually plug in the phone, flip on Dual-Mount SD, or mount the SD card as a drive, and copy them over. With AirDroid, as long as the phone's got an internet connection I can pull up my photos and paste them into a document, put a bunch into a zip file, and/or export or import them all while my phone is downstairs (and I'm upstairs).
You can upload notification sounds, alarms, and ringtones, setting the default with a mouse click. You can also remove old ringtones you no longer want, or bundle up a bunch of them so you can send them to a friend.
AirDroid requires no special software on the PC/Mac side, as it's all done in a web browser.
You can see what apps are installed and remove them, send them to a friend, install APKs directly from your computer without using ADB or call up the trusty old web market link, play music that's on your phone through your computer, see your call logs, use text messaging via web page in a slightly more elegant format than Google Voice, and manage the files and folders on your phone with a browser.
Although our EVOs are awesome, sometimes a mouse and a keyboard can really help speed things up, and the AirDroid desktop is incredibly useful helping with that. The only thing I wish this had was the ability to mirror what is on the screen, but that would probably require a rooted device.