Toy building systems including adjustable connector clips, building planks, and panels

A building set, comprising:

• one or more planks, at least one of which includes a first face, an opposing second face, a first side, an opposed second side, a first end, and an opposed second end, the at least one plank including a thickness defined between opposed faces, opposed sides, or opposed ends;
• one or more first connector clips, at least one of the connector clips including a clip body and a plank engaging channel, the channel of the clip including:
• a base defining a floor;
• first and second substantially parallel extensions, each including interior surfaces, the extensions extending distally from the base and defining a channel therebetween into which the thickness defined between opposed faces, opposed sides, or opposed ends of the plank is receivable, a width of the channel being substantially equal to the thickness of the plank that is receivable within the channel so that the extensions pinch the thickness of the plank received within the channel, frictionally coupling the connector clip to a plank received within the channel;
• and
• wherein the at least one plank includes a round hole formed through the thickness between the faces.