Here's the open source SoftPLC software - there’s bit of setup at the beginning, but basically you download the Codesys V3.5 development system:
https://store.codesys.com/codesys.html
Plug in a Raspberry Pi on a network such that you can ping it from your development computer, then go to "Update Raspberry Pi" on the Codesys Tools menu, then you're off. You can code in ladder logic, structured text, or function blocks, and it's got a really easy web visualization module, so you can set up HMI screens on a web server on the Pi. I'm planning on using one to run some home automation stuff via a web page back at my house, like remotely turn on the lights, heat up the hot tub, etc. It's amazingly capable for a $35 Pi. It'll run for 2 hours for free for testing, or for $60 you can get a license to run the Pi as a PLC indefinitely.
I'm using it to translate my Profinet encoders to Ethernet/IP on the Allen Bradley side, but the Pi can record data trends and display it on a web page all by itself if needed.
Let me know if you have any questions.
Wade