The RideNow Project is designed to help individuals within a group or organization coordinate ad hoc shared rides. This paper describes three design decisions the RideNow team made in order to allow incremental adoption and evolution and to capitalize on local conditions. (1) The system allows users to interact with the system through email or Web, because we anticipate that email will be most convenient when there are few users but the Web interface will be more useful as the number of users increase. (2) The system does not force structure on user-entered data such as dates, times, and locations, instead allowing conventions to emerge. (3) We use the group’s shared physical spaces to provide additional information about ride sharing activity. Categories and Subject Descriptors D.2.2 [Software Engineering]: Design Tools and Techniques General Terms Design Keywords Social Computing, Design Methods