I've found this somewhere - might have been /r/worldbuilding - and figured it'd be good to share. I'm not a person who builds worlds for fun - I get very attached to my works, and I have already too many worlds to fit a new one in without a very good reason - but, perhaps, some people might enjoy it.
Source code for the generator is available.
The generator gives you a set amount of challenges for you to complete on your own, with each challenge containing a bonus objective which isn't directly attached to the main challenge but is related to it: for example, describe a group of people living in the city mentioned in the challenge whose motives aren't entirely clear.
It isn't big on the bases for challenges, but maybe the Hubski community can contribute and expand it.
Maybe we can do weekly worldbuilding prompts, like we do daily with writing.
Oh man, this thing is cool. I'd definitely be down for worldbuilding prompts, too. It's really helpful to hear other people's ideas with things like this.