An Inventor's Licence, aka Compulsory Licensing, is a form of intellectual property protection found under Irish law, and the law of several other states *there*. It's basic intent is similar to that of patents *here*, but its implementation leads to quite contrary results.
As with patents, the aim of inventor's licences is to encourage invention and the sharing of knowledge. Also, when something is invented, the inventor registers their invention with the Office of Public Record.
The key difference between a patent and an inventor's licence is that it is not possible for a licence holder to stop somebody from reproducing their invention so long as the product is faithful to or an improvement upon the original design. If somebody builds something covered by an inventor's licence, they must pay the holder a proportion of net profit in return.