Gosoapbox.com is a back channel web program, working in real-time, that engages students. It allows them to ask questions, during or after your teaching and learning session. It is very easy to setup. Just sign up, login and setup a soapbox for a teaching group. An events code is automatically generated which is assigned to the teaching group. Give this event code to students; they login using the events code only and can start asking questions. Silly comments can be deleted. You can also poll students. Easy.
Today, during my observed year 9 lesson we obviously had the silly remarks as expected, but once they had got this out of their system, it worked really well, and impressed the two observers in my lesson! Consequently, I used it again with my year 12 students and they loved it, asking/answering exam questions at the end of my session. I think it is good for assessment, and encouraging students to work together and share ideas. I recommend you try it out!