Universal Building Set
A Universal Building Set is a Lego set designed to form the habit of building multiple different models using the same elements. It comes with instructions for building several example models, to encourage the builder to also come up with their own ideas.
It's essentially a subtheme of both Basic and Technic, with Technic set 8020 looking like a comparatively more modern version of Basic set 744, complete with motorisable vehicles and a windmill.
When the Basic theme evolved into Creator, the Universal Building Set subtheme evolved into 3 in 1.
Lego themes: Lego Basic | Lego Creator | Lego Homemaker | Lego Technic | Legoland | Universal Building Set