WinDivert 1.1: Windows Packet Divert

 Windows Packet Divert (WinDivert) is a user-mode packet capture-and-divert package for Windows Vista, Windows 2008, Windows 7, Windows 8.

WinDivert allows user-mode applications to capture/modify/drop network packets sent to/from the Windows network stack. In summary, WinDivert can:

• capture network packets
• filter/drop network packets
• sniff network packets
• (re)inject network packets
• modify network packets

WinDivert can be used to implement user-mode packet filters, packet sniffers, firewalls, NAT, VPNs, tunneling applications, etc.
The main features of WinDivert include:

• packet interception, sniffing, or dropping modes
• supports loopback (localhost) traffic
• full IPv6 support
• network layer
• simple yet powerful API
• high-level filtering language
• filter priorities
• silent installation

freely available under the terms of the GNU Lesser General Public License (LGPL)

http://reqrypt.org/windivert.html