Lerdge makes a decent set of 3d-printer mainboards, starting with the lerdge-s, which is the low end, the lerdge-x, which is apparently a higher version, and the lerdge-k. One thing I like about them is that though they have a number of capabilities, the X in particular lets you add on, for instance, ESP32 WIFI support, or ethernet, or USB host support, or additional extruders. You choose the hardware modules that fit your needs and add them in. 

THe lerdge-k, btw, appears to basically be a lerdge-x with all the modules. 

A color screen, touch support, etc - there's not much to dislike about it. 

Except the firmware. 

The firmware is buggy, closed source. I couldn't change things, fix things, break things if I wanted to.

And I wanted to. 

I'd had some success with Monoprice boards figuring out exactly how the hardware worked and porting Marlin 2.0 to them. Since Marlin already supports a few different STM32F4 processor boards, in this case, it would be a matter of working out the pins to get the most basic support running.

I snagged a killer deal, paying ~35 bucks for a lerdge-x with no driver chips, and began digging.