Ogg Vorbis is the patent-free lossy format that came out of the free software world. It compresses well and it has always been unencumbered, which is why games, Wikipedia and open-source projects reach for it while consumer hardware mostly ignores it.
Every conversion below runs in this page, on your own machine. Nothing is uploaded, there is no queue, and there is no account to make. Pick a target format, or just drop an OGG file above and choose afterwards.