I've been maintaining a process control and automation platform called Krill for quite a while and I use it to automate everything in my life with RPi.

The idea behind Krill is it's not an event driven system, it's built with an "Observer Pattern". It has over 40 "Node" types where a node has a single function - send an email, call a web hook, control a GPIO Pin, read a serial device etc. A node fires and does its job and completes. Any other node in the system on any server can observe a node fired in real time and in turn, execute it's single purpose and so on. I have lots of Pis and bigger servers all acting as a mesh on my network.

For this project I used a "Task List" node which in Krill can track tasks with due dates and if they go past due the node fires. I have three GPIO Pin nodes configured to observe the Task List and based on the priority of an overdue task an LED lights up.

The Button is configured as an Input Pin Node and the Task Lists observe it, so when pressed it resets all overdue tasks. This is an easy build and setup to get more annoying the longer a task is past due like sound a buzzer or have an actuator bonk me on the head 😄 - call it "the reminder app that smacks you when you procrastinate"

In this project I 3D printed this enclosure to house a RPi 3 LEDs and a momentary button and the Pi is running Krill Server:

I built Krill with Kotlin Multi-Platform so there's an app for every platform. In the App this is what it looks like - the low priority task node has a past due item so it's list and the green LED is on (you can see pin 11 glowing a little indicating it's state is high): 

Krill can do a boatload of functions but I like to boil it down to simple use cases like this and the reminder box is actually pretty handy. This took about an hour to make and just apt install krill krill-pi4j on the pi after adding my repo.

Feel free to AMA I post projects like this regularly here.