GeeXLab 0.19.0.0 has been released for all platforms: Windows, macOS, Linux and Raspberry Pi.
Newbie here. Is there any offline reference available, or any pdf export or anything.
Sorry, there is no offline doc available.
But you can read these short articles to get an idea of how GeeXLab works:
You can also test and modify the learn code samples available in the full code sample pack (http://www.geeks3d.com/dl/show/385) (in the learn/ folder).
And the reference quide for all functions: http://www.geeks3d.com/geexlab/reference/