Software in the Public Interest provides a fiscal home for a number of FOSS projects like Debian and FFmpeg: https://spi-inc.org/donations/
The Open Source Initiative [disclosure: I recently served on its board] maintains the Open Source Definition, a list of approved open source licenses, educates about open source, and much more: https://opensource.org/membership
The Electronic Frontier Foundation advocates for privacy, security, and digital liberties: https://supporters.eff.org/donate/join-eff-today
The Freedom of the Press Foundation protects whistleblowers and journalists with free software like SecureDrop
and education and advocacy: https://freedom.press/donate/
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