Searching: Tool to manage and create conditional actions

Hi you heroes :slight_smile:

i am looking for an easy way to manage custom behaviour of my site.
In the way of if this than that... if date of event is due in 3 days, send a defined reminder mail to all attendees.

So i'm looking for some kind of rules-engine, that runs as backend-task AND is able to react on direct calls (as kind of filter)
And i want to hook it easily into existing hooks (by some kind of selection out of existing action hooks)

Can you help me with that?