Delta T
Voron 008
Wilson II
Prusa I3 Rework

Most 3D printers have similarities but each design has its own strengths and weaknesses. From the speed of a Delta to the positional accuracy of the Core X-Y and the ease of design and troubleshooting of the Cartesian, learning about the operation and kinematics behind all the designs can give insights into many aspects of mechanical design and software/electrical engineering.