UnrealIRCd

UnrealIRCd is an open‑source IRC server written in C that runs on Linux, BSD, Windows and macOS. It has been in continuous use since 1999 and currently powers a large share of public IRC networks. The software emphasizes modularity and security, offering a highly configurable configuration file and a range of built‑in protections such as advanced anti‑flood, anti‑spam, cloaking and GeoIP lookup.

The server implements full IRCv3 support, SSL/TLS encryption, JSON‑RPC interfaces and remote include capabilities, allowing operators to extend functionality through modules. Regular stable releases are provided in the 6.x series, with recent updates adding features like multiline support, conditional configuration, and a new GeoIP engine, while maintaining compatibility with a wide variety of Unix‑like systems and Windows builds.

Documentation, FAQs, and community support are hosted online, and users can obtain assistance via an IRC support channel or the project forums. The code is released under GPL‑2.0, is self‑hostable, and does not require any subscription or tiered licensing.