[1] The initial implementation ran under Mac OS and Microsoft MS-DOS, and provided basic DEC VT102 terminal emulation with support for multiple simultaneous connections and an FTP client.
Over time, the program evolved with added features and revisions to the user interface.
Support for Tektronix 4010/4014 vector terminal emulation and a protocol for downloading and viewing raster images were added.
NCSA Telnet originally used a built-in TCP/IP protocol stack to communicate over the network.
As standard APIs became available for network communication, the program was adapted to use them, most notably Apple's MacTCP.