DNP3 (IEEE-1815) protocol stack. Modern C++ with bindings for .NET and Java.
A C++ implementation of the TinyLEGO cryptographic protocol [NST17] for general secure two-party computation
C++ implementation of SIP, ICE, TURN and related protocols.
Performance comparison of the most popular C++ serialization protocols such as Cap'n'Proto, FastBinaryEncoding, Flatbuffers, Protobuf, JSON
A C++ implementation of the FAST protocol.
mailio is a cross platform C++ library for MIME format and SMTP, POP3 and IMAP protocols. It is based on standard C++ 17 and Boost library.