AppSec Labs Advanced Packet Editor

Advanced Packet Editor (APE) is an open source packet editor for viewing and editing TCP and HTTP communication.
APE can attach itself to a process to get intercept communication between a server and a client
APE uses filters, both external (using python scripts) and internal for automatically substituting text on the fly or simply injecting/editing request and responses.
APE is easy to use and configure!

The advanced packet editor is based on the original Packet Editor (http://www.packeteditor.com/)

Source can be found here: https://github.com/appsec-labs/Advanced_Packet_Editor