URL: http://www.icdia.co.uk/
It provides you with lots of technical background information, downloads, overviews and other resources on CD-i.
URL: https://retrostuff.org/category/philips/cdi/
Dedicated to repair, modification and in-depth articles of the CD-i systems and related hardware.
URL: https://www.theworldofcdi.com/
Blog and forum covering everything CD-i related.