What apps can be linked with DT3 and DTTG? Is it possible to automate tasks using IFTTT or Zapier?
This isn’t possible.
Sort of - depends how you view it
There is indeed no direct integration between Zapier and Devonthink. But you can achieve essentially the same effect by using a Devonthink indexed Dropbox folder and smart rules:
Obviously I can’t remember everything in the 54.500 posts I’ve read so far
Plus the combination of Dropbox Indexing, Smart Rules, and Scripting create possibilities which even you as the designer never anticipated - which is terrific problem to have!