It's called "Audacity"
Here's the link: Clicky!
I think most people know about Audacity. However if they don't it's a very good free alternative to the commercial editors.
Have you tried Wavosaur? It's supposed to be lighter on system resources.
Wavosaur has all the features to edit audio (cut, copy, paste, etc.) produce music loops, analyze, record, batch convert.
Wavosaur supports VST plugins, ASIO driver, multichannel wav files, real time effect processing. The program has no installer and doesn't write in the registry. Use it as a free mp3 editor, for mastering, sound design. The Wavosaur freeware audio editor works on Windows 98, Windows XP and Windows Vista.
Features:
http://www.wavosaur.com/features.php
Downloads:
If I had to choose between Wavosaur and Audacity, I'd choose Audacity everytime. I've used Wavosaur before, and even posted about it in the freeware thread, however it doesn't like very large wav files -- like a whole audio CD worth.