FFMpeg is a good, free (gpl) software only available for Windows, that is p. As a bonus, it doesn’t consume tons of CPU power, so it can run on just about any computer. Audacity is the default software for several multimedia content creators because not only is it free, it’s also relatively easy to use.
Source code and user manuals for some old versions are available on FossHub, as well as AppImages since version 3.0.3.