Wow. Great free site where you can create polls and online quizes. They can be embedded into your website and voting can be restricted to one vote per person. Lots of great possibilities.
An interesting article about how to use Twitter as a classroom tool. I use it mostly for PD. I tried having hashtag discussions on Twitter this year with my senior English classes but the kids don't seem to use it too much. They prefer to text people they know rather than have a discussion with lesser known classmates.