He has developed and popularized a number of Internet technologies since the late 1980s, including the Gopher protocol, Uniform Resource Locators (URLs), and POPmail.

[4][5][6][7] Gopher's menu-based hypermedia combined with full-text search engines paved the way for the popularization of the World Wide Web and was the de facto standard for Internet information systems in the early to mid 1990s.

[2] Working with other pioneers such as Tim Berners-Lee, Marc Andreessen, Alan Emtage and Peter J. Deutsch (creators of Archie) and Jon Postel, McCahill was involved in creating and codifying the standard for Uniform Resource Locators (URLs).

[8] In the mid 90s, McCahill's team developed GopherVR, a 3D user interface for the Gopher protocol to explore how spatial metaphors could be used to organize information and create social spaces.

[12] In a 2016 interview with Leo Laporte, McCahill said that his involvement with developing the Croquet Project had led him into contact with Second Life and that he had become interested in the sociology of virtual worlds.