NodeBB is a next generation of community platform/forum software, with more customizable features and a mature plugin system that extends the abilities of standard forums. NodeBB...
Discourse is a Civilized Discourse Construction Kit, a free, flexible, fundamental building block for online discussion communities of any size, tiny to huge.
AsmBB is written in assembly language and uses FastCGI in order to reach the higher possible performance and scalability.
Fast, minimalistic, modern comenting and discussion system.
Fruum is an open-source embeddable communication solution for discussions, documentation and more.