We have have been on self-hosted Heptapod [1] for about a year without much complaint. Heptapod is a fork of GitLab with Mercurial support. For open source projects, there is a free hosted version [2].
[1]: https://heptapod.net/ [2]: https://foss.heptapod.net/
Other hosting options can be found on Mercurial's Wiki page on hosting [3].