I mean, open source projects can be started or based in the US. But that doesn’t mean it’s an American project; it’s just that the people who started it happened to be American.

I guess if we had to point to a specific American OSS, maybe Tor would qualify? It was initially developed by the CIA, so that may qualify it as US OSS. But it has since taken on a life of its own and the CIA doesn’t have any hand in active development anymore… So it’s still hard to say that even “being made by the literal US government” qualifies an OSS project as “American”.

It’s sort of a Ship of Theseus situation. At what point in the development process do we consider it a non-American project?

There definitely are FOSS projects run by the US government: Ghidra is an open source reverse engineering tool developed by the NSA.

I think the majority