Bounce offers free and dead-simple website capture and annotation for hassle-free sharing of site-related notes.
Visit Bounce, plug in a URL, and Bounce snaps a screenshot of the website you pointed it at. Once the capture is loaded you can draw boxes around elements of the site you want to annotate and immediately add text. When you share the URL for your capture others can check out your notes by mousing over the focus boxes you've created.
Bounce is a free service and requires no registration. Have a simple tool for sharing annotated screenshots? Let's hear about it in the comments.