In the past I've donated old hardware to OpenBSD [1] and would love to donate to them directly, but they aren't registered as a 501c3 in the US and can't claim the deduction on taxes (yes, I know, I am not 100% altruistic).
Instead I donate to FreeBSD and support OpenBSD in an ancillary way through OpenBSD Amsterdam [2]. Which yes, is also not tax exempt, but does comes with nice OpenBSD VM.