https://github.com/nmap/npcap
https://nmap.org/npcap/
https://nmap.org/npcap/guide/
http://www.tcpdump.org/pcap.html
https://github.com/jpr5/ngrep
https://en.wikipedia.org/wiki/List_of_IP_protocol_numbers

High-level, multiplatform C++ network packet sniffing and crafting library.
https://github.com/mfontanini/libtins

PcapPlusPlus is a multiplatform C++ network sniffing and packet parsing and crafting framework.
https://github.com/seladb/PcapPlusPlus

A high level C++ network packet sniffing and crafting library.
https://github.com/pellegre/libcrafter

Header only packet analysis library written in C++11
https://github.com/slankdev/libpgen

Moloch is an open source, large scale, full packet capturing, indexing, and database system.
https://github.com/aol/moloch

Like nmap for mapping wifi networks you're not connected to, plus device tracking
https://github.com/calebmadrigal/trackerjacker

Malicious traffic detection system
https://github.com/stamparm/maltrail

https://github.com/chengr28/Pcap_DNSProxy

https://github.com/basil00/Divert