Fusion TCP/IP
- Commercial embedded TCP/IP stack written in C.
- http://www.unicoi.com/fusion_net/fusion_tcp_ip.htm

EZ Stack Embeddable TCP/IP Protocol Suite
- Commercial TCP/IP stack designed for the ZiLOG eZ80F91 microcontroller.
- http://www.ezstack.com

NicheStack
- A commercial TCP/IP implementation for embedded systems.
- http://www.iniche.com/nichestack.php

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.
- http://www.sics.se/~adam/uip/

Miniweb
- Tiny proof-of-concept combined implementations of TCP and HTTP.
- http://www.sics.se/~adam/miniweb/

sevenstax
- Commercial TCP/IP implementation for embedded processors.
- http://www.sevenstax.com

ejip
- A very minimal TCP/IP stack in Java, meant as a proof-of-concept for embedded systems.
- http://www.jopdesign.com/ejip/

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.
- http://www.unusualresearch.com/tinytcp/tinytcp.htm

FutureTCP
- FutureTCP is a commercial implementation of TCP.
- http://www.futsoft.com/tcp.htm

CMX-MicroNet TCP/IP Networking
- Commercial TCP/IP stack for 8-bit and 16-bit embedded processors.
- http://www.cmx.com/micronet.htm

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.
- http://www.sics.se/~adam/lwip/

TCP-BFA
- Implementation from Stanford; TCP Buffer Fill Avoidance.
- http://klamath.stanford.edu/publications/HPNC98.pdf

TCP Santa Cruz
- An implementation aimed at improving TCP congestion control over internets with heterogeneous transmission media.
- http://www.cse.ucsc.edu/~chris/sctcp/sctcp.html

OpenBSD's TCP implementation
- Based on TCP in 4.4BSD.
- ftp://ftp.OpenBSD.org/pub/OpenBSD/src/sys/netinet/

NetBSD's TCP implementation
- Based on TCP in 4.4BSD.
- ftp://ftp.NetBSD.org/pub/NetBSD/NetBSD-release/src/sys/netinet/

FreeBSD's TCP implementation
- Based on TCP in 4.4BSD.
- ftp://ftp.FreeBSD.org/pub/FreeBSD/FreeBSD-stable/src/sys/netinet/

SCPS-TP
- A suite of protocols aimed at space users. Includes an implementation of a protocol extending TCP.
- http://www.scps.org/scps/

Xinu TCP implementation
- The implementation of TCP used in Comer's Xinu Unix-like operating system.
- ftp://ftp.cs.purdue.edu/pub/Xinu/

Experience with TCP Vegas from SunOS 4.1.3 to NetBSD 1.0
- Including source code, descriptions of experiments, and links to other TCP Vegas resources.
- http://netweb.usc.edu/yaxu/Vegas/Html/vegas.html

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.
- http://tcp-impl.grc.nasa.gov/