I'm hoping someone was smarter than I am and bookmarked these 2 terrific fics. Neither is very long, and I'm almost positive I read both on AO3 but have not been able to find either of them. In the first, Tony built a lightsaber, it was a team fic, I think (not sure if it was purely gen or slash/pre-slash Steve/Tony), and at first Steve was disapproving, but then he saw how much fun they were though ultimately Fury proves to be a killjoy. In the second, Tony builds a sonic screwdriver. That is all I remember about that one.
Any help much appreciated!
ETA: Found, in comments, by monicaop--Thank you!