WA2
From ASSS Wiki
.wa2 files are sound files for the game Subspace/Continuum. They are simply .wav files with the extension renamed. Continuum can also recognize the .wav extension, so you needn't bother renaming files when making LVZ.
It is known that Continuum cannot support 4bit .wa2 files.
You can use tools such as Microsoft Sound Recorder to make basic edits to sound files. Just right click on a .wav file and select Record from the menu.