CoRE - SmartThings Rules Engine
Smartthings has a simple built-in rule engine and there are few rule engines that can be installed as SmartApps. Among all of them CoRE is a sophisticated and free rules engine that can be used for almost everything.
CoRE is a very powerful community – created rules engine for SmartThings. It allows you to set up stacked conditionals like "If A then B but only while C and not if D."
Setting it up can be quite complex, but there are many community members who will be glad to help you. Here is the post from the author.
There's also extensive documentation on CoRE in the community-created SmartThings wiki.
Since CoRE is not an official smartapp it should be installed through github which might look like a complicated process, but there are clear instructions in the Wiki and also in the community forum. Once you learn how to write new rules using CoRE there is no end to your creativity to make your home smarter than ever.
Few samples from the community forum to show the power of CoRE
1. Switches Modes depending on the time of day and presence.
2. Notify if the dog had already been fed twice that day and he picked up the dog bowl for third time.