"Programmable Fax" - as if fax was somehow not accessible to computers before twilio invented a proprietary API for it. Yes, it was, believe it or not: You can indeed send faxes from software, via a fax modem connected to a landline, or an ISDN TA connected to an ISDN line, via a GSM MT connected to a GSM network ...
Or, if you like your internet and don't want to deal with older communications networks directly, there even is a frickin non-proprietary API for it that was standardised nearly two decades ago: T.37 and T.38. And there have been companies offering gateway services that allow you to send faxes to the PSTN using those APIs for about as long.