Llama 2
Meta released the weights openly and permitted commercial use, doing so with Microsoft as the main distribution partner.
Why it matters
A large company deliberately gave away a capable model for the first time, moving the open-weights argument from research into commerce.
The licence is not open in the classical sense: it forbids use by services with more than 700 million users and restricts applications. Open source practitioners objected to the term being used at all. In practice Llama 2 became the basis for thousands of products and for most open models of the next two years.