Retractable in the sense that you have the ability to retract the tip back into the sleeve via twist, via click eraser, via button. I hope I make a little sense. Also, I apologize regarding my horrific response time.
Those are called double knocks. Plenty of models discussed on the forum, take a look! Lightest weight models are probably the almost fully plastic ones like the Ohto double knock/Niji grip 500. The Colleen Jibs are probably also among the lightest, because they are super small.