This app is called activity center. This is my Fully functional, once deployed web-app.

#login/registration features, encryted, input entered against data in DB,create a new activity, join other users activity, activity cannot be created before today. A pre-existing acitivty can be joined by others. A creator may leave his/her own activity leaving it open for others to join. A user cannot join a new acitivity while the duration overlap. #Only the creator can delete an activity when both conditions are true 1. only creator can delete and 2. delete works only if there is no other participant in that particular activity.