GASP stands for ‘Generator and Analyzer System for Protocols’. It allows you to decode and encode any protocols you specify. The main use is to test network applications : you can construct packets by hand and test the behavior of your program when faced with strange packets.
You can download it from the following link: https://packetstormsecurity.com/files/download/10207/gasp-0.90.tar.gz
Source: https://packetstormsecurity.com/files/10207/gasp-0.90.tar.gz.html