This article examines the characteristics of collaborative work and overlapping activity systems in the popular online game World of Warcraft. Using genre theory and activity theory as frames to work out the genre ecology of gameplay, the article focuses on how players coordinate ad hoc grouping activity across and through genres. It articulates the related development of open systems in online gaming in a discussion of interface modifications (AddOns) and online information databases that players generate, drawing on De Certeau's formulation of strategies and tactics and Warner's discussion of publics and counterpublics. The article concludes by discussing implications of online gaming for an open-systems approach to information design in professional communication and for professional communication in general.