spinics.net is mostly mailing list archives these days

github is where over 100 million developers shape the future of software, together. contribute to the open source community, manage your git repositories, review code like a pro, track bugs and features, power your ci/cd and devops workflows, and secure code before you commit it.

stack overflow is the largest, most trusted online community for developers to learn, share​ ​their programming ​knowledge, and build their careers.

openbenchmarking.org is an open, collaborative testing platform designed by phoronix media and the developers behind the phoronix test suite, the most comprehensive benchmarking platform for linux, bsd, and other operating systems.