What to do with old prototypes

Hi all,

Just wanted to know what everyone does with their prototypes once they're done with them. I find myself making several versions of the same thing, and then not knowing what to do with the older versions once I've corrected/improved on them. I don't want to keep them because my space is already crowded as it is, but I also don't want to give them away as I don't want to put something that I'm not perfectly proud of out into the world. Throwing them out seems... wasteful, especially for something that once had a life.

What do you all do with your prototypes? Do you keep them? Give them away? Is there somewhere that will take leather scraps for recycling?

Thank you!