Superexpert (https://superexpert.ai, demo space: https://demo.superexpert.ai and download: https://github.com/Superexpert/superexpert-ai) allows the creation of custom chatbots. Open source, it can be deployed locally on a computer, with the APIs of the language models or a model installed. Document databases or RAGs can be added.
A documentation/tutorials page is available for installation: https://superexpert.ai/docs/

The online demo allows the creation and use without allowing the addition of documents. 15 language models are available in this demo (Open AI, Anthropic and Google). 5 chatbots created during the tests (no limit indicated, unlimited?).

The configuration, although in English, is easily understandable and the settings are numerous (tutorial for creating a chatbot: https://superexpert.ai/docs/quick-start).