Out there on the wild seas of the Internet, you’ll discover many islands existing in the form of the automotive forum. Some islands are bountiful, while others are inhabited by angry folks who believe that the cherished idol they pray too is the only one that matters. Across all of these island forums is one constant, however, and that’s the fact that many potentially great vehicles are being offered up for sale… and you might be missing out on a lot of them. That’s where HiddenRides.com comes in.
Touting itself as being built by “two dudes who loves cars”. The site was built as a shared passion experiment for all the enthusiasts out there endlessly turning over page after page of forum classifieds.
The site aggregates listings from all of the forums, and offers it all up in an easily filterable listings page. Check out HiddenRides.com and prepare to waste a bit of e-Time as you hunt down whatever it is you’re looking for… you might just find it on one of those random islands adrift in the iSea.
[Updated: I asked the owners a few questions and they responded below]

-How did you come up with this idea?
Building something in the auto universe has been decades in the making – my brother and I always loved cars (childhood bedroom wall was a collage of 90s sports cars), so naturally we spent a lot of our time browsing through car forums.
The idea was spurred by two things: 
1) Inspiration: Missing out on an Oxford Green/Cinnamon E46 M3 6spd by a few hours
2) Light Bulb Moment: Discovering WatchRecon (a watch classifieds search engine) – we wanted to build a similar tool for car enthusiasts
After validating the product with a couple friends, forum members, etc – we decided to pull the trigger and do this thing.
-Is it just you?
It’s two people – myself (Brian) and my brother (Kevin).
-Was it easy to code/script?
In one word, no. We started it with curiosity and naivety, but soon learned how monumental the task was. 
To have the website that you see, we had to have many different apps, servers, and services.
Scraping and parsing the unstructured data was an incredibly challenging task, and we definitely consider that the secret sauce here 🙂
There’s also a lot of other stuff going on under the hood like ElasticSearch, image processing, and computer vision (e.g, detecting cars in images).
It’s not perfect and it’s still a work in progress.
-How often does it update?
The scraper runs twice a day, and you can expect to see new results every day. As we  increase the number of forums, the listing count also grows.
-Can you restrict to block certain forums? Say if you hate what a given group routinely posts?
Yes, we have that capability but we are actually looking to expand the list/sources at the moment. 
We are currently tracking hundreds of forum classifieds sections and growing the list every day.
There is also some smart filtering going on – i.e. skips spam and posts that do not have photos or other basic information.