Reddit is likewise another competitor.
I've always looked at many of the subreddits as a potential for different products or a channel to access customers of that interest.
For example:
* r/RedditGetsDrawn -- Marketplace for artists and users
* r/SomebodyMakeThis -- Request for product
* r/DataIsBeautiful -- Collection of people passionate about data visualization
* r/IAMA -- Ask Me Anything -- many other community sites have copied this concept.