“hackamajig” is about projects and artwork in papercrafting, woodworking, metalworking, electronics, robotics, coding, … in short, hand-made nerdcraft.
We use the term “hack” to denote clever and often absurd constructs and off-the-cuff problem solving or trade tricks. Related terms are “kink” (used by machinists in the first half of the twentieth center, but it fell out fashion) and “bodge” (which the Brits like, but which hasn’t really caught-on in the States).
The folks at sugru express this in a way we really like:
I don’t want to buy new stuff all the time. I want to hack the stuff I already have so it works better for me.