Are you getting paid for your work? You mentioned "free prototypes". You could always just write on your resume that you worked for "X Company", and then give

Are you getting paid for your work? You mentioned "free prototypes". You could always just write on your resume that you worked for "X Company", and then give details about the project you worked on, whether or not it sees the light of day is irrelevant. Employers want to see that you can work/code/do your job, not if past projects were a success or not.