Can the EG91 run user applications on the module?

I am new to Quectel and have not had too much luck searching the website. I am wondering if a user application can be made to run on the EG91 module. Is there an SDK? C-compiler? What processor, operating system, etc.? Or can it only communicate via USB/Serial/etc. to a separate external host processor? There must be some basic information on this, if it is possible. I’ve seen vague references to ThreadX, Linux, and QuecOpen(?), but I have no idea if any of this is related to the EG91.

Thank you.