While doing my research on non-profits who do sponsorship of OS software projects, I came across Linux International. They seem like an interesting group. Apparently they do not put any restrictions on who may apply for development grants. They do state that all grants must be accounted for and specifically targeted (e.g., hardware purchases or paying for documentation writings), but I see no mention of the software needing to be developed under the control of a non-profit in order to be able to qualify.
So, it would not hurt to apply. Their email address is:
grant-submissions-info _at_ li.org
It looks like their only restriction is that the software must be made freely available so that the Linux community at large will benefit -- which is what we do anyway :-).
This organization looks interesting. They have some well-known sponsorships, including IBM and HP.
I have no idea what the size of the grants are that they give out, but it may be an opportunity for some OS developers to get that extra few dollars to keep their project afloat.