Wavosaur

Wavosoaur is a powerful, free audio editor which combines all the standard audio and sound editing capabilities you would expect plus the ability to use VST plugins, real-time processing, audio stream input-output (ASIO) drivers.  It runs independently so does not require any installation.

Features:

• Supports all standard editing functions (cut, paste, copy, mix, replace - all in a non-destructive manner) and processing options (conversions, inserting silence, volume changes, fades, flips and normalization)
• Advanced features include the ability to batch process, export files to other programs (Matlab, PSpice, Excel) resample, remove vocals, crossfade, region detection, auto trim clips, remove silence and export multiple WAVs.
• Analysis features include frequency analysis, RMS power and a variety of synthesis features (waveform generator frequency swap and impulse train).
• Special features such as slicing and auto-slicing as well as multipoint envelope editing. 
• Provides Visual Studio Technology (VST) support enabling real-time tweaking and playback, ability to load/save presets and VST effects.
• The software is portable (under 2mb) and does not require installation (no impact on the registry) and works across a number of different Windows versions (98, XP, Vista)

A fully featured audio editing packaged which is free to download and provides a wealth of tools.  It combines standard editing features with a series of advanced capabilities such as VST processing, audio analysis, and specialist features. 

Provides a wealth of standard editing features and VST support.

It's tiny download size, "what you see is what you get" interface, lack of installation requirement and packed feature set means that it is non-destructive audio editing can start straight away at zero cost.  The support for ASIO means you can experience low latency so you don't experience lag when you're recording and editing. 

Wavosaur is ad-free and comes with a number skins which allow you customize the look and feel to your own preferences.