These are alternative stores or tools that allow you to download applications without having to go through the official stores, giving you the advantage of not tracking your data and keeping you informed when new updates are available.
But yes, you can also download some applications from GitHub.
Not bad.
But the reputation thing is a bottleneck for people who already trades big amounts.
I guess they're going to do it musig too, like the desktop app.
Hope it happens soon.