resource recommendations - What are good sources for Open-Source fonts?

What are good sources for Open-Source fonts?

Note that by "Open-Source" I don't mean only free, but truly "open, free to modify and published under an Open Source license" fonts. These are still very rare.

I know of two:

Any others?

Answer

Google font directory https://www.google.com/fonts

The fonts are free (as in beer and as in speech). Most of them are using the SIL Open Font License, but not all of them.