Is this an addon that is here?

Don't think it is, might be custom made.

It looks a bit like https://www.gmodstore.com/market/view/sh-pointshop although, if it is then it's definitely modified.

Alright thank you guys :), Will just stick with the good old pointshop 2 since nothing else seems to have surfaced as good.

I'm pretty sure I've seen this menu when playing "F2S: Stronghold", not sure if it's part of that gamemode or just a third party addon.