These guys, http://faxzero.com/, offer two free fax transmissions per day. No software to install.
This organization offers free faxes too. I've used them in the past; however, coverage is not universal.
http://www.tpc.int/tpc_home.html
Great for those without fax machines... or land lines...
Tags: voip, faxing, facsimile, scan, fax machine