I admit to pretty much always liking the general idea of cricut machines. Use them with a regular pen to draw, cut a variety of materials, I could easily see a circuit mask pen and etch tank doing some lightweight PCB design.
But every time I saw one, I looked at how you needed cartridges with designs and shrugged, said "Not today."
The cartridges were no doubt something I COULD reverse engineer and mimc...but why? Then I saw a cricut expression for twenty bucks, delivered and said "This is the time."
I knew about the FreeExpression project and dove into the documentation quickly. I didn't have an ISP, but I did have an arduino as ISP, and with a little work was able to build the code.
It didn't work on my machine.
The display never lit up, and I got only one string from the usart before it went silent.
And I hated having to program using the ISP. Upload from PlatformIO or Arduino didn't work, because there's a time window where you have to initiate the connection.
And that just had to go.
First step - I cloned MegaCore and modified their optiboot to look for the STOP button on boot, and if so, wait forever.
Eventually I opened a PR to Optibook, here - https://github.com/Optiboot/optiboot/pull/352
This allowed me to hold "stop" on power on and have an unlimited window to flash.
A good enough start.