http://pierovggsterf4w5xplynqtl56srftc242l3g2xloqlty6nv7372xuyd.onion
Mozilla has existed for a long time, and this is definitely visible in the integration of the development tools they use. However, some of them are kinda unique, particularly their SCM: Mercurial. Today, open source is almost a git monoculture, and it is the versioning system I have used most of the time.