Lex got this construction set called Crazy Action Contraptions for Christmas. It’s like Lego Technics, I think, but has instructions for a bunch of different contraptions you can build using the included pieces. He love sit! He has built all of them several times. The include things like a zip line, a “Tennessee Time Killer,” several different zip cars, and this crazy doodler thing (I forget the exact name of it.)
Totally useless contraptions, but he’s having a great time with them!