We describe an annotation tool developed to assist in the creation of multimodal actioncommunication corpora from on-line massively multi-player games, or MMGs. MMGs typically involve groups of players (5-30) who control their avatars 1, perform various activities (questing, competing, fighting, etc.) and communicate via chat or speech using assumed screen names. We collected a corpus of 48 group quests in Second Life that jointly involved 206 players who generated over 30,000 messages in quasisynchronous chat during approximately 140 hours of recorded action. Multiple levels of coordinated annotation of this corpus (dialogue, movements, touch, gaze, wear, etc) are required in order to support development of automated predictors of selected real-life social and demographic characteristics of the players. The annotation tool presented in this paper was developed to enable efficient and accurate annotation of all dimensions simultaneously.