GPT4All by Nomic AI is one of the most accessible ways to run LLMs locally. It offers a simple desktop app (Windows, macOS, Linux), supports dozens of models, runs on CPU (no GPU required), and includes a local API server compatible with the OpenAI spec. GPT4All is designed for non-technical users and developers alike, with built-in document Q&A and LocalDocs features.
Free and open-source. Hardware costs only.