To make the hunt for smart apps that other community members have written easier, the community-created wiki has quick browse links by tag for the “community-created” sections of the forum. So you can look at just a list of Smartapps for lighting, or security, or alerts, etc.:
That said, if you have an iOS device, SmartRules is a third-party rules engine app which does make things much easier for many use cases. I found the $10 price tag well worth it.:
For another alternative, as was mentioned, CoRE is a free community-created rules engine currently in the early design stages. Very powerful, very sophisticated, but also can be challenging to use. And since it’s in such early stages, you may have to occasionally delete everything you’ve set up and reenter it. Still you get a chance to help influence the design. And just as importantly for this thread, it demonstrates just how complex and/or logic can get in smartthings if you do you start writing custom code.
So the capabilities are there, it’s just with the exception of smart rules, they aren’t available with an intuitive interface: