Kantai Collection, also known as Kancolle, is an online browser game in which one assumes the role of an admiral, assembles a fleet of ship girls, girls based on World War II era Japanese (and as of a few days ago, also german) ships and submarines, and battles against fleets of alien enemy warships.
There are four official manga spin-offs (Though the only one people actually care about is the 4-koma), and an anime adaption in the works, as well as mountains of fanworks.
Kancolle is as addictive as it is not-really-fun-at-all-but-it-has-cute-girls-so-who-cares. I've been playing on-and-off since October, currently trying to craft hachi.
Anyone else here who plays this?