4.4BSD-Lite2 TCP/IP stack implementation
This is the implementation that arguably most modern implementations are based on. Even though one of FreeBSD, OpenBSD, NetBSD, or BSD/OS would be used today rather than actual 4.4BSD, this code remains to a very large extent the reference implementation of TCP.
CMX-MicroNet TCP/IP Networking
Commercial TCP/IP stack for 8-bit and 16-bit embedded processors.
CPC/IP
CPC/IP is an implementation of the PPP, SLIP, IP, ICMP, UDP, TCP, DNS, TFTP, HTTP, ping, finger and telnet protocols for Amstrad CPC computers with an Amstrad, Pace or CPC Amstrad International serial interface. The code occupies about 14K, excluding the serial, filing system and IP buffers.
eCos
Free embedded OS (Linux-based); includes a tiny TCP/IP stack.
ejip
A very minimal TCP/IP stack in Java, meant as a proof-of-concept for embedded systems.
Elmic Systems Turbo-Treck
Commercial dual-stack (IPv4/IPv6) embedded TCP/IP implementation.
Experience with TCP Vegas from SunOS 4.1.3 to NetB
Including source code, descriptions of experiments, and links to other TCP Vegas resources.
EZ Stack Embeddable TCP/IP Protocol Suite
Commercial TCP/IP stack designed for the ZiLOG eZ80F91 microcontroller.
FreeBSD's TCP implementation
Based on TCP in 4.4BSD.
Fusion TCP/IP
Commercial embedded TCP/IP stack written in C.
lwIP - A Lightweight TCP/IP stack
lwIP is a lightweight implementation of the TCP/IP protocol stack. The focus of the lwIP TCP/IP implementation is to reduce RAM usage.
Miniweb
Tiny proof-of-concept combined implementations of TCP and HTTP.
NetBSD's TCP implementation
Based on TCP in 4.4BSD.
NicheStack
A commercial TCP/IP implementation for embedded systems.
OpenBSD's TCP implementation
Based on TCP in 4.4BSD.
OpenTCP
An open-source (BSD-style license) implementation of TCP/IP for 8- and 16-bit microcontrollers.
SCPS-TP
A suite of protocols aimed at space users. Includes an implementation of a protocol extending TCP.
TCP Implementation WG Mail Archive
The IETF tcpimpl working group was shut down in Sep 2000, but the mailing list still exists. Historic archive may also be of interest.
TCP Santa Cruz
An implementation aimed at improving TCP congestion control over internets with heterogeneous transmission media.
TCP-BFA
Implementation from Stanford; TCP Buffer Fill Avoidance.
The uIP TCP/IP Stack for Embedded Microcontrollers
An implementation of the TCP/IP protocol stack that uses very little resources. Code size is on the order of a few kilobytes and memory usage is on the order of a few hundreds of bytes.
TinyTCP/TinyFTP
A simple implementation of TCP & FTP, suitable for burning into ROM. It is, in effect, a hack put together in two or three days written in C--in 1986.
Xinu TCP implementation
The implementation of TCP used in Comer's Xinu Unix-like operating system.