The mini-services part refers to the fact that each high-level feature - git & hg repos, CI, bug trackers, etc - is implemented as its own standalone web application. The composable part is that you can freely use them in concert with each other to whatever extent is appropriate for your project. Consider that on GitHub, GitLab, etc, one project == one git repo == one bug tracker == one path for merge requests == one wiki == etc. SourceHut's upstream codebase, on the contrary, has several git repos, one mailing list, several CI configs, N bugtrackers where N != nrepos, and so on.