Install docs: https://forge-allura.apache.org/docs/getting_started/install...
I agree that sourceforge.net as a service might not be my favourite, but Allura the forge-software seems pretty good. I think the only thing that comes close is the stack from Canonical -- but Allura seems more viable to self-host (and scale up when needed -- rather than "only a vm" or "full cluster"). It also seems less "overly opinionated", and still includes sensible defaults (contrast with getting up and running with Trac).
YMMV, but it doesn't look half-bad. Right now I don't need anything more than what you can easily get with either a separate wiki+mercurial+mailing-list, "just" trac or fossil -- but for something in-between "too big to host internally" and "too complex for Trac to be easy" -- it looks rather interesting. I'd love to hear any war stories.