No, it is based on UbuntuMate

Just for clarity, what is INDI crew in your opinion?

They are essentially the same but handled differently.
Also AB is free and SM is not.
I personally prefer SM but that doesn't mean that AB is inferior.
Both are well supported in this forum.
With AB you would need to do more Linux gymnastics than with SM in my opinion.

And they are both based on Raspbian now.

No you are wrong, Stellarmate is based on Raspbian and has been fro some time now....

Yes you are correct.....

And the APT repositories were are placed?

Dont understand the question....if there is one...
SM is now based on raspbian and so is AB, and they have been for a while,

INDI packages is found in PPA UBUNTU repository sudo add-apt-repository ppa:mutlaqja/ppa, but if it is not based on Raspbian, where are located the packages?

AIUI if you aren't using a Ubuntu based system then there is no repository, you need to compile from sources.

IIRC AstroBerry at least doesn't recommend this because it may mess up the AB install which could be older than the current souces. They see themselves as providing a stable system rather one that has the latest bells and whistles.

I run plain Raspbian and use AstroPi3 to manage installing or updating the Astro components.

Not sure what benefit there is to the multitude of dfferent flavours of Linux and different UIs and distributions. Looking at Ubuntu Mate and Raspbian the differences don't seem to be more than cosmetic.

I think i've heard that the Raspbian distrbution isn't suited to other people hooking into it and the Ubntu one is better in that respect.

Jasem has set up his own repository on a server to hold the packages, same as the author of Astroberry.... clever guys...

This is also not true, there are raspbian repositories for both SM and AB, you update and install just the same as you did on Ubuntu, the authors of both have created the repositories on there own servers for this purpose, so the end user see no difference....

Ok, which is the address of raspbian repository??