All you need is an internet connection and your fax service account.
No tedious web interfaces, no sending faxes via email attachments business. Well integrated you can send your documents straight from your print dialog. Pick the recipient from your addressbook or just type in the number. Fossi will send your fax in the background and let you know about the result. The faxes window provides an overview of past and current faxes.
Mac OS X 10.4 or higher.