So there are the obvious ones, such as putting a float valve in your ATO container (if applicable) and having it e-mail you a day before it runs dry.
In this case, I simply made a virtual outlet called RefillATO:
Set OFF
If Sw3 OPEN Then ON
Then, under my e-mail alarms, I simply have this line of code
If Output RefillATO = ON Then ON
Defer 001:00 Then ON
You can use a similar setup for alerts for any dosing containers or have float valves if the level in your sump is getting too low, too high, etc. I also have one to alert me whenever my saltwater mixing container is running low and will need to be refilled.
The other quick and easy project you might enjoy is to set up some analog switches for common tasks you might do.
For example, I have a project box on my stand where I can hit a switch and quickly kill all the pumps in the tank. This was primarily designed for cases where there is an emergency and I don't want to waste time with messing with apex fusion, but I will also use this if I need to take a still picture of a coral or any situations where I need to go into the tank and don't want any flow.
Same idea, where I have a virtual outlet called NoPumps:
Set OFF
If Sw2 OPEN Then ON
Then for each pump (e.g. skimmer), I simply insert this line:
If Output nopumps = ON Then OFF
I also use the same analog switches to turn off my white LEDs and T5s, so I can easily have only actinics showing if I have someone over and want to show the corals only under actinic.
Lastly, if you have available channels, you can easily make an ATO with an optical sensor or buy sensors to make a cheap LDK sensor without needing to buy the module/Apex sensors.