I think "works" can include digital artifacts — to my understanding, this was part of the Mozilla Foundation's rationale for exemption. But Mozilla's "public work" was the Internet as a free platform, not just some piece of software used by some unidentified group of people. Mozilla compared the Internet to a public road, and depicted its role in maintaining the Web as a free and open platform as being similar to ensuring that roads are well-kept and accessible to everyone.
Yorba's application appears to have been more along the lines of, "We make free software. Poor people can use free software and other programmers can learn from it." (I'm basing this on the IRS's response — I can't find a full copy of Yorba's application anywhere.) So I can kind of see why that appears less compelling from a "public works" perspective to the IRS.
> Software is not a public work. The development and distribution of software is not a public work even if published under open source or creative commons compatible licenses because software is not a facility ordinarily charitable to include "erecting or maintaining public buildings, monuments, or works." This language slightly broadens the original formulation from four centuries ago.
It goes on to quote the Charitable Uses Act of 1601.
Sure, if "maintaining a work" counted, the standard would be pretty easy to meet!
But it's not just "works" but "public works." As in, "a broad category of infrastructure projects, financed and constructed by the government, for recreational, employment, and health and safety uses in the greater community." http://en.wikipedia.org/wiki/Public_works (Yes, it's Wikipedia, but this definition is about right.)
Can't immediately find any IRS documents defining the term, but here is the definition from Black's Law Dictionary:
> Structures (such as roads or dams) built by the government for public use and paid for by public funds.
There is also a maxim of statutory interpretation in law that a word it known by its fellows. In this case, that would mean preferring an interpretation of "public works" that yields a certain kinship between that term and "public building" and "monuments." This would seem to militate in favor of the Black's/Wikipedia definition. Note also that these three are followed by "lessening the burdens of government" which might be another hint. (I.e., organizations that support public works are deserving of tax exempt status because they lessen the burdens of government.)
I can also tell you anecdotally that, at least among lawyers, the term is very well known and is definitely widely understood as having the definition given by Black's and Wikipedia. There may be a creative argument to be made that an open source project is a public work (could make a fun law review article!), but I doubt it would go very far.
I'd say Yorba falls under that if you take "works" to include digital artifacts.