Scapy is a powerful interactive Python-based packet manipulation tool used by penetration testers to create, modify, send, and analyze custom packets. It supports many protocols and allows you to set TCP flags, sequence numbers, and more.

tcprelay is used to redirect TCP traffic, not to craft packets.

Bluecrack is used for cracking Bluetooth encryption, irrelevant in this context.

tcpdump is a packet capture tool, not suitable for crafting or injecting packets.