Where can I find the mappings for current :EMOJICODE: systems (Slack, Discord, iOS, Android, etc.)?

[BingeCode]

Even the much referenced WEBFX Emoji Cheatsheet doesn't list its source or mappings. Github does, but I want to find out which code system is the most popular/used one - or rather which one's exist. I want to build an application that allows anyone to use emojicode in any application and any os and would appreciate any pointers in the right direction as to where I can find more information about the various mappings that exist already.