There are no such sites currently.
That site is for builds, not for add-ons.
Very true. It would be nice to have another system like that however. Maybe someday it will become an actual project.The website portion wouldn't be too hard, but the in-game manager would be trickier.
The in-game downloader would be easy once you wrote a useful API on the server side. Port was actually working on something like this, called BAM, but it died.
Try remaking this post in the "Add-Ons" section, not because im a complaining bitch, but because more addon experienced people look there, instead of here general discussion.
I'm going to just imagine, with my very little knowledge about Torquescript, that this is easier said than done.