Probably the most unique thing about Urbis was their system for generating reviews which I thought was pretty interesting -- reviews on your work were locked by default. In order to unlock a review, you had to write a review of equal word count on someone else's work. I thought this was pretty successful method for incentivizing active participation on the site, something I haven't seen replicated anywhere else. Although I more or less grew out of writing recreationally, so I wouldn't even know if there were a successful modern alternative to Urbis.