Implementations

EasySoap++
A cross platform C++ implementation of the SOAP 1.1 specification.
http://easysoap.sourceforge.net/

Fusion SOAP
Implementation of embedded SOAP Client/Server in C language. [Commercial]
http://www.unicoi.com/fusion_web/fusion_xml_soap_client_server.htm

gSOAP
A cross-platform C and C++ implementation. Generates C/C++ source codes for Web service and client applications.
http://www.cs.fsu.edu/~engelen/soap.html

IBM SOAP4J
A Java implementation of the SOAP protocol. It has been superseded by Apache SOAP. By IBM.
http://www.alphaworks.ibm.com/tech/soap4j

PEAR::Package::SOAP
This is a soap integration for PHP (pear package).
http://pear.php.net/package-info.php?pacid=87

pocketSOAP
A COM implementation of SOAP client facilities. Originally targeted at PocketPC platform and now also targets Wintel. By Simon Fell.
http://www.pocketsoap.com/pocketsoap/

4S4C
Aka Simon's SOAP Server Services For COM, a COM component that will invoke methods on COM objects, from a SOAP request message, and return the results as a SOAP response message. By Simon Fell.
http://www.4s4c.com/4s4c/

SOAP::Lite for Perl
Implementation of SOAP in Perl, includes modules for XMLRPC and UDDI. By Paul Kulchenko.
http://www.soaplite.com/

Spheon JSOAP
Implementation of SOAP 1.1 (Server and Client) for Java.
http://sourceforge.net/projects/spheon-jsoap/

TclSOAP
An implementation of the SOAP protocol in the Tcl scripting language.
http://tclsoap.sourceforge.net/

White Mesa SOAP Service Implementation
SOAP implementation as a Windows NT service. Supports WSDL. By Robert Cunnings.
http://www.whitemesa.com/wmsoapsvc_about.htm

Wingfoot SOAP
A Lightweight implementation of SOAP 1.1 for J2ME (CLDC and CDC).
http://www.wingfoot.com/products.html

XSOAP toolkit (a.k.a. SoapRMI)
Implementation of RMI for Java and C++. By SoapTeam, Extreme Computing Lab.
http://www.extreme.indiana.edu/xgws/xsoap/