I am a really big fan of Agenda and love how I was able to make it part of my day in day out routine. I am also a big Shift (Shift - Productivity Made Simple) user and they allow differents apps to work within its system. It would be amazing if somehow Agenda could becamoe an app I can integrate with Shift!
Thanks for the feedback!
Agenda does already have quite a few ways to integrate with other apps. They are described in Shortcuts - Agenda Community
We support URL schemes and native Shortcuts. It could be the Shift can already work with Agenda in that way, I am not sure. Agenda does work very well with Hookmark, for example, which is also about integration of apps.