Re: issue/bug management, project management, people management, product management all in one, preferably open source software ?

I think the closest you would get to a single product for all that is a single suite of products which are reasonably well-integrated. issue, project, and product management are almost always combined unless you are just using github issue tracking or the like. Jira certainly covers all of those.  And it will integrate with vanilla git, though you will lose functionality compared to the integrations with github and bitbucket simply because vanilla git lacks features compared to those.  The rest of the atlassian product suite adds plenty of functionality around the rest of the stuff you are asking for.  But it's hard to imagine you haven't already considered atlassian, so I assume you are looking for a recommendation for something other than that, but I can't think of anything I've used that is actually better (and I say that as someone who doesn't really like Jira, either). It's a pretty low bar, admittedly.

Jira is one of those products, like SalesForce, which is enormously powerful, but only after you've customized the heck out of it because that is how it is intended to be used.  Massively flexible, configurable, and automatable, the setup out of the box is far from optimal for most teams.  You really have to know what you want and tell the software how to set itself up to support that. And it helps if you have an agile-esque project management methodology as it is certainly developed with that in mind. It isn't going to dictate to you how to manage issues, projects, and products. It will very flexibly allow you to set it up to work with it in almost any way you like - but you have to have someone become something of an expert in the platform AND you have to have a very concrete understanding of exactly how you want to use it or you end up with the wishy washy, not very effective project and issue management workflows dictated by the default configuration, which is very lowest common denominator.