From FreeSWITCH Wiki
Short for "Zapata Telephony"
Zaptel refers to Jim Dixon's open computer telephony hardware driver API. Zaptel drivers were first released for BSD and Jim's Tormenta series of DIY T1 interface cards. Digium later produced interface cards from Jim's designs and improved the Zaptel drivers on the Linux platform. Digium then added further drivers also following the Zaptel API for other telephony hardware.
The Zapata Telephony project was named after Emiliano Zapata, a Mexican revolutionary, indicating the revolutionizing nature of the Zaptel project. For more details see http://www.zapatatelephony.org.
Excerpted from voip-info.org
See also: OpenZAP