They have an extensive GitHub full of stuff. What portions are not open source?

Is this like "OpenRouter" where they don't have any of the core product actually available?

It seems their main app is proprietary. See https://lmstudio.ai/app-terms#restrictions-on-use. Example excerpt--though many of the other points in the ToS also makes it very un-FLOSS:

>> You agree that You will not permit any third party to, and You will not itself:[..] (e) reverse engineer, decompile, disassemble, or otherwise attempt to derive the source code for the Software[..]

What’s the best open source alternative?

Jan: https://www.jan.ai/

LibreChat with vLLM?

https://www.librechat.ai/docs/configuration/librechat_yaml/a...

llama.cpp

To add a few more details: llama.ccp now both has a web ui out of the box that even supports model switching, and easy model file downloads from huggingface using the cli: '-hf name_of_model:the_quant_you_want'.