With a land line, many computer and all-in-one printers are capable of sending and receiving faxes. Even without a land line, there are many paid services including eFax and InterFAX which allow you to send and receive faxes from your computer.
If you only send the occasional fax and don’t need to receive them, FaxZero allow you fax a document for free without even having to set up an account. There is one catch; there’s an ad on the cover page. For $2.00, though, you can send a fax without an ad.