Solderpad Hardware License
Apache License 2.0 adapted for silicon – the default permissive licence for open RISC-V cores.
Solderpad takes the Apache text and widens its definitions to cover hardware description code, mask works and physical products. Apache's patent grant comes along, which is the point: in semiconductors, patents rather than copyright are the real exposure.
Version SHL-0.51 became the de facto standard for academic and industrial RISC-V work. ETH Zürich and Bologna's PULP platform, lowRISC and Google's OpenTitan security chip all use it. The choice says something about the industry: where software spent decades arguing about copyleft, hardware people went permissive almost immediately, because no fab customer wants to risk publishing an entire chip layout because one block was reciprocally licensed.