If you have a large site with many teams, then a good way to do this is to ask the teams to produce a 2-3 minute vidoe of gameplay which they can talk over. This keeps the presetations short and concice, and minimises technical issues. The vidoes can also be uploaded on the project pages of GGJ website! If already uploaded to YouTube, all the vidoes can be made into a playlist, and played through one computer (meaning no need for annoying HDMI converters or projector techincal problems).