Add MindMac to productivity section

[hugo53]

0. I have read the Contribution Guidelines
1. Project URL: https://mindmac.app/
2. Why should this project be added: Being used by 1000+ users around the world, MindMac is a feature-rich & privacy-first native ChatGPT app that allows to use OpenAI, Azure OpenAI, Anthropic Claude, OpenRouter all in one place. I think it's helpful for repository's audiences.
3. End all descriptions with a full stop/period
4. Entry is ordered alphabetically
5. Appropriate icon(s) added if applicable (OSS, freeware)

[iCHAIT]

@herrbischoff @dkhamsing any thoughts on this?

[herrbischoff]

I'm opposed to everything OpenAI/ChatGPT, so I'm not impartial on this. My vote is no.

[hugo53]

@herrbischoff I got your point, and I just want to clarify by adding some information. MindMac is a comprehensive native macOS application that not only supports OpenAI, but also many other generative AI model providers like Google AI, Google Vertex AI, Anthropic Claude, Cohere, Perplexity, OpenRouter, and upcoming support for Mistral on Dec 18, 2023, and any local LLMs. It offers a superior user experience for those who rely on AI assistants for their daily tasks.