SCREEN ANNOTATION
Jing Project
When you're working with designers and developers, Jing is an amazing free collaboration tool to put annotations or request changes into their mock ups. You can also record your voice while you explain how you want things to be done. It captures what you see on your desktop while recording it.
Jing provides the basic visual elements in making your suggestions as clear as possible to your designers. You can directly upload your capture to screencast.com where your staff can view it easily.
Though Jing is a free tool, there are some paid features that you can also exploit to gain better advantage. The good thing is, it also works both for PC & Mac.