The problem with Fossil is lack of a driving force. GitHub is so successful because it is non-trivial to get Git working. Now that Git is a standard, there's a lot of copycats for GitHub itself, because every developer knows Git.*
Fossil seems to be pretty easy to use all by itself, hence there's no service similar to GitHub, because the added value would be considerably smaller, plus you'll be going up against the giants like Git and GitHub; in fact, Bitbucket has already abandoned Mercurial support recently, embracing the monoculture of Git. If anyone's more interested in Fossil, http://fossil-scm.org/ website itself runs on Fossil (yes, it's self-hosted, and, yes, Fossil itself comes with a CMS, as well as a bug-tracking system), but there's also https://src.fossil.netbsd.org/ — the timeline interface is claimed to be the best feature of Fossil, it provides great visual representation of commits on all the branches as they happen; e.g., https://src.fossil.netbsd.org/timeline?n=50&b=2020-01-02+15:42:26 (in case there's nothing on branches on this link, see http://archive.is/dmKxZ , or http://web.archive.org/web/20200107001225/https://src.fossil.netbsd.org/timeline?n=50&b=2020-01-02+15:42:26 , which shows exactly which release branches were updated at what time and in what order). The other key difference of Fossil compared to Git is that the whole history of work is permanent, not transient like in Git's branch and squash-merge model, e.g., you don't just remove things (like branches) from the repository that were there yesterday, like in Git, and unlike in CVS or many other systems. Does it mean OpenBSD and/or NetBSD should switch to Fossil? No, that's not what I said. Cheers, Constantine. http://cm.su/
