Open source hardware
Physical designs whose drawings, schematics and board files are published so anyone may study, modify, manufacture and sell them.
The Open Source Hardware Definition 1.0 appeared in 2011, deliberately modelled on the Open Source Definition. OSHWA was founded the following year and has run a certification programme since 2016, handing each approved project a serial number. Arduino and RepRap are the canonical examples; Adafruit and SparkFun built businesses on the idea.
Legally it is messier than software. Copyright protects the drawing but barely the finished product, so a copyleft clause may in practice only bind the documentation – someone manufacturing a copy needs nobody's permission unless a patent gets in the way. Hence dedicated licences like CERN-OHL and Solderpad, written to cover "making" rather than just "copying". The definition is also explicit about editable formats: a PDF of a schematic does not count.