NCSA Telnet is an implementation of the TELNET

TELNET

Telnet is a network protocol used on the Internet or local area networks to provide a bidirectional interactive text-oriented communications facility using a virtual terminal connection...

 protocol created at the University of Illinois at Urbana-Champaign

University of Illinois at Urbana-Champaign

The University of Illinois at Urbana–Champaign is a large public research-intensive university in the state of Illinois, United States. It is the flagship campus of the University of Illinois system...

 National Center for Supercomputing Applications

National Center for Supercomputing Applications

The National Center for Supercomputing Applications is an American state-federal partnership to develop and deploy national-scale cyberinfrastructure that advances science and engineering. NCSA operates as a unit of the University of Illinois at Urbana-Champaign but it provides high-performance...

 in 1986 and continuously developed until 1995. The initial implementation ran under Mac OS

Mac OS

Mac OS is a series of graphical user interface-based operating systems developed by Apple Inc. for their Macintosh line of computer systems. The Macintosh user experience is credited with popularizing the graphical user interface...

 and Microsoft MS-DOS

MS-DOS

MS-DOS is an operating system for x86-based personal computers. It was the most commonly used member of the DOS family of operating systems, and was the main operating system for IBM PC compatible personal computers during the 1980s to the mid 1990s, until it was gradually superseded by operating...

 and provided basic DEC VT102 terminal emulation as well as support for multiple simultaneous connections and an internal FTP

File Transfer Protocol

File Transfer Protocol is a standard network protocol used to transfer files from one host to another host over a TCP-based network, such as the Internet. FTP is built on a client-server architecture and utilizes separate control and data connections between the client and server...

 server. At the time, NCSA Telnet was the first implementation of telnet for the Macintosh or a PC that provided the ability to connect to multiple hosts simultaneously.

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.

In 1987, a short-lived version for Sun Microsystems

Sun Microsystems

Sun Microsystems, Inc. was a company that sold :computers, computer components, :computer software, and :information technology services. Sun was founded on February 24, 1982...

 SunOS

SunOS

SunOS is a version of the Unix operating system developed by Sun Microsystems for their workstation and server computer systems. The SunOS name is usually only used to refer to versions 1.0 to 4.1.4 of SunOS...

 was released.

Although the PC version of NCSA Telnet lost popularity once Microsoft Windows was in widespread use, the Macintosh

Macintosh

The Macintosh , or Mac, is a series of several lines of personal computers designed, developed, and marketed by Apple Inc. The first Macintosh was introduced by Apple's then-chairman Steve Jobs on January 24, 1984; it was the first commercially successful personal computer to feature a mouse and a...

 version remained in use throughout the 1990s as a basic tool of connectivity in academic and commercial installations.

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 those methods, most notably Apple's MacTCP

MacTCP

MacTCP was the standard TCP/IP implementation for the Macintosh operating system through version 7.5.1. It was the first application-independent implementation of a TCP stack for a non-Unix platform and predates Winsock by over 5 years...

. However, the built-in stack (one of the few completely independently developed TCP/IP stacks in use at the time) continued to ship in the software for years.

NCSA Telnet was released as open source

Open source

The term open source describes practices in production and development that promote access to the end product's source materials. Some consider open source a philosophy, others consider it a pragmatic methodology...

 software (although the term had yet to be coined at the time) and as such spawned a number of spin-off products including

• BetterTelnet
• Brown tn3270
• BYUTelnet
• InterCon
  InterCon Systems Corporation
  InterCon Systems Corporation was founded in April 1988 by Kurt D. Baumann and Mikki Barry to produce software to connect Macintosh computers to other computers. At the time, there was no real concept of the Internet and there was still a question of whether the TCP/IP protocols or OSI protocols...
  
  's TCP/Connect series
• MacBlue Telnet (Chinese language version)
• MacTelnet
• NCSA Telnet-J (Japanese language version)