Twiddle This! A collaborative writing tool.

"Twiddla calls itself a web-based meeting playground. Not only is it a fun way to swap ideas about a website or image, it’s incredibly useful as well."

—webworkerdaily.com
Browse websites in a shared, real-time whiteboard, while marking them up, sharing files, and chatting along. It's called co-browsing; all the cool kids are doing it.