I wish Google would open up an API for Google Now to developers. There are many custom notifications that I would love to add to my Now screen, but right now I am limited to the few that Google provides.
that would last about 5 minutes before Now turned into another ad platform.
https://developers.google.com/gmail/actions/google-now
From the other direction, you can have Google Now call back into your Android app, triggered by hot words, as demonstrated in the new version of Todoist:
https://todoist.com/blog/2013/11/todoist-for-android-adds-su...
I can't find any published API for the latter.