Online web app to plan events

Think it should work similar to [login to view URL] but of course completely different use. I want to use mine for events. But I really like the interface and the timer and ability to people to join to submit their answers. My app is for planning events. So use case would be I create an event and send it out to people and people respond within a time limit. It's really simple I think... like planning poker. I will do designs in wireframe and you use that to build. Features: 1. Login system 2. timer function 3. email notification function 4. saving past events 5. ability to post an event to facebook or twitter. so integration with facebook and twitter 6. create an event (description, image, address) and people can see who has accepted thats about it. Budget is around $200-$250.