Online Office

For some reason, I've never been too fond of applets. Maybe because I saw too many bad examples on how to use an applet. However, my opinion changed dramatically, when I saw ThinkFree Office. Basically, it's the regular office you are used to, but inside an applet!!
You have Word, Excel and PowerPoint with all the features you can imagine. It's truly amazing how similar it is to the real thing. It works so good you could use it to substitute the real Office and save a few disk space. Just create a free account, and you get 30Mb of space for creating docs, spreadsheets, convert them to pdf, etc. Try the demo and see for yourself! One of the things that amazed me: you can even do fullscreen slideshows of powerpoints :)
Apart the usefulness, it's really the best applet I've seen.