The closest thing that I've come across is the (in?)famous phpBB garage mod. However, that is, as its name implies, a very specific application. I'm thinking more of a general collections mod that can be used for anything from coins to stamps to cars.
Taking the coins for example, users can submit information on each of their coins under their own "collection." Collections can be viewed in a separate section much like phpBB Gallery. You'd have the obligatory recent additions, random, new, etc. complete with comments capability, rating, etc.
Given the broad nature of this mod, the ACP is where I'd envision the meat to be. You'd have to be able to define the fields for the main collection submission page and also allow these fields to be searchable when viewing the Collections.
Now the phpBB Garage includes a ton of other modules including dealer you bought car from, dyno run stats, parts, etc etc. Not sure that the ability to add additional modules is really necessary. Really, the core of phpBB Garage can be the backbone of this mod.
(You're probably saying why not just use Garage? Well I have and spent a ridiculous amount of time modifying it to suit a collection that is far from cars. The modifications were half baked at best and at the end of the day, that is not a validated mod - actually I think it's been abandoned more than once.)