FaxZero is a free online fax service, allowing the user to send .doc or .pdf files, up to three pages each, two faxes a day. An ad goes on the cover page. (Can you live with that? I can.)
In some dealings with insurance-related bureaucracy over the past few weeks, I've been asked several times to fax necessary paperwork. (And I've wanted to ask: Is it still the 20th century?) When I explain that I don't have easy access to a fax machine and offer to scan a page and send a .pdf, the answer is No. So I'm happy to now know about FaxZero. FaxZero also offers unfree faxing, with no ads.
FaxZero ("Send a fax for free to anywhere in the U.S. and Canada")