Felix Rieseberg (Anthropic, ElectronJS) has released a free Mac app designed to help people build their own LLMs from scratch.

Announcement tweet here.

Direct link: Language Model Builder

From the site: "Using the default settings, you’ll get a model that writes coherent, grammatical multi-paragraph text in as little as a day. On a MacBook Pro M5 Max you could train a GPT-2-small-class model (~100–150M parameters on a few billion tokens) in about a week. It might be obvious, but to avoid disappointment: you will not train a Claude Fable 5 or ChatGPT 5.6 Sol in your garage."