Reaper is a comprehensive piece of audio production software (for Windows, Mac, and Linux) offering a full multitrack audio and MIDI recording, editing, processing, mixing and mastering toolset. You could use it to record voice acting for your game, to edit sound effects to sound more futuristic, or to put together a soundtrack.
- Check out the Reaper user guide (PDF)
- Reaper have also produced some step by step videos on how to use the tool.
- Get the tool here.