Yuuguu's approach to screen-sharing goes straight through your instant messaging clients, although they're not required to run the program. It's a multiprotocol messaging program that supports the biggest IM services--Yahoo, MSN, Google, AIM, ICQ, and Skype--in the hopes that rolling the services into one package will appeal to resource-conscience users.
When you want to initiate a sharing session, you click on the users' name and share the provided code. As with its competitors, both sides must agree to the share before it can begin. Unfortunately, Yuuguu doesn't support file-sharing, although you can transfer files via IM.
Yuuguu users can share with as many as 29 others, but only the host needs to have the software installed. Participants can watch and contribute to the chat, making this an effective tool for small-scale presentations. It supports voice chat, too. Of the various screen-sharing apps out there, Yuuguu's instant-messaging support makes it among the most Web 2.0-esque of the bunch. If those features are what you need, Yuuguu's a good choice for you.