Software

IPv6 Software Resources
Patches for different applications.
http://www.version6.net/

The Kame Project
Project to develop IPv6 and IPsec stack for use in BSD-based operating systems. Included in the OpenBSD sources since OpenBSD 2.7 Release.
http://www.kame.net

Linux + IPv6 HOWTO by Peter Bieringer
The goal of the Linux IPv6 HOWTO is to answer both basic and advanced questions about IPv6 on the Linux operating system. This HOWTO will provide the reader with enough information to install, configure, and use IPv6 applications on Linux machines.
http://en.tldp.org/HOWTO/Linux+IPv6-HOWTO/

Microsoft IPv6
Microsoft is developing support for Internet Protocol version 6 (IPv6), a suite of standard protocols that will become the next generation of network layer protocols for the Internet. IPv6 represents the future of networking. The new protocol is designed to solve many of the problems of the current version of IP (known as IPv4) with regard to address depletion, security, autoconfiguration, and extensibility.
http://technet.microsoft.com/en-us/network/bb530961.aspx

Peter Bieringer's IPv6 and Linux
Status of the implementation of IPv6 in Linux and the cookbook for setting up IPv6 on Linux.
http://www.bieringer.de/linux/IPv6/

Quake 2 IPv6 - patch code by Viagenie
Quake 2 by IdSoftware patched Viagenie to support IPv6
http://www.viagenie.qc.ca/en/ipv6/quake2/ipv6-quake2.shtml