In the last few years,representing and promoting your work,especially teaching something like photoshop tutorials using screencasts became very essential and popular for us.By this way,we can reach to thousands of people by uploading the videos to Youtube like websites.The below screencasting  tools are all free for screen recording but of course their features are not as much as paid ones.Some of them are web-based and some of them are softwares to use lifetime.Anyway,you can easily record your screen and add audio or edit your recorded screen videos with these tools.If you know more free tools then please tell me commenting so we can add into the list.