Question for someone who follows this space: are there any significant models/tech/etc that OpenAI has made open? Either before or after they changed business models. What they've kept private is well-known, but are there any checkboxes in the other column?

Whisper. Speech recognition and translation. Probably the best general-purpose speech recognition available right now. Certainly the best you can run on your own hardware. Open-sourced code and publicly free and available models. https://github.com/openai/whisper