Stable Diffusion
The image generator that made open-weight AI art mainstream, released publicly in 2022 and still the base for a huge amount of community tooling.
Stable Diffusion is a text-to-image model released in 2022 by Stability AI, together with LMU Munich and the non-profit LAION, which supplied the training data. The important thing was not that it made pictures from words, since other systems already did that. The important thing was that the weights were published. Anyone could download the model, run it on a home graphics card, inspect it, fine-tune it, and build products on it without asking permission.
That decision shaped everything that followed. A whole ecosystem of interfaces, fine-tuned variants and add-on techniques grew around it, and the phrase open-weight model entered ordinary conversation. It also put the copyright question about training data on the public agenda, because for the first time people could see exactly which dataset a popular model had been trained on.