Subreddits are, perhaps, reddit’s biggest strength. Introduced in 2008, they’re a huge part of the reason why the site rose to popularity, and why that popularity has yet to taper off.

Want a community for something you like? Build a subreddit. Don’t like the current popular subreddit for that thing? Screw it, build a new one. Anyone can build one — and as long as the subreddit’s content stays legal and abides by the site’s TOS, reddit’s staff generally doesn’t get involved with administrating what goes on there.

It’s easy for one huge community to die almost overnight (see: Digg). But a community made up of a zillion sub-communities? That’s a different beast.

But finding new subreddits to join can be a pain. After you’ve found the subreddits for your hobbies and favorite TV shows, most people only stumble into a new subreddit when someone else mentions it in a comment. Many users, meanwhile, end up subscribing only to the handful of subreddits that reddit puts all new users in by default.

Seemingly trying to combat this, reddit has just starting rolling out a “trending subreddit” feature. It’s unclear if this change is permanent, but it seems to be showing up for most (if not all) users.

The idea: each day, reddit will algorithmically select a half dozen or so non-default subreddits that have seen a particularly high amount of activity lately, and list them at the top of the front page.

Right now, for example, they’re highlighting /r/oddlysatisfying (which collects images of things that are inexplicably satisfying), /r/JapaneseGameShows (which is mostly clips from, you guessed it, Japanese game shows), /r/smashbros (which blew up this week after Nintendo released a bunch of new details about the WiiU Smash Bros release), /r/minimalism, and /r/GameOfThrones.

Based on the submission history of the bots that power the feature, it looks like they’ve been fiddling with their trending algorithms in a semi-public space since at least April 1st

While it’s a handy new feature for users, it’s a pretty clever business move, too. Despite its massive userbase, reddit still isn’t profitable. Advertising to specific communities — like, say, all of /r/GameOfThrones — is one of reddit’s more straightforward revenue streams… but it only really works when lots of subreddits have enough members to make an ad worthwhile. If they can make up-and-coming subreddits grow even faster, everybody wins.

Another clever decision: the trending bar shows up even when a user isn’t logged in. Its a quick, non-obtrusive way of saying to new users, “Hey — there’s more going on here than what’s listed on the front page.”

Update: reddit has officially announced the new feature by way of their changelog, and addressed a few user concerns: