Cross-Platform C++ GUI Library

Aleth – Ethereum C++ client, tools and libraries

The Haiku operating system. (Pull requests will be ignored; patches may be sent to https://review.haiku-os.org).

Fast Ethereum Virtual Machine implementation

A compiler frontend for the C programming language

Doug McIlroy's C++ regular expression matching library

BEware, Another Mailer - an e-mail client for BeOS/Haiku