Waveshare is a component electronics retailer which sells everything you'd need to build a death ray. They sell a bunch of OLED and LCD screens in various sizes, and they recently added an epaper screen to their catalog.
The 4.3inch e-Paper (that is both the name and part number) module features a 4.3" epaper screen (800 x 600 resolution, 2-bit). According to the support docs, the module is designed to work both as a screen and as a standalone display. It packs in a 72MHz CPU, 128MB Flash storage, and a microSD card slot.
That's not a whole lot of processing power, but it's more than enough to drive the screen. Plug this module into an Arduino board and it will be able to cycle through its library of screen images on command. (I'm less certain that it will be able to display new images as quickly.)
The 4.3inch e-Paper is designed to communicate with other devices over a 6-wire serial port. It can work with Arduino and other DIY kits like the Raspberry Pi, and if you get a USB to serial board you can also program it from your PC (software and source code samples are included in the resource kit).
This module is not the first DIY component with an epaper screen, but it is the first to use a "knockoff" epaper screen from Guanzhou OED, E-ink's Chinese competitor.
While the e-Paper Hat and most other DIY modules use an E-ink screen manufactured by Pervasive Display, this module was built-to-order by Waveform and boasts a higher resolution screen than any other epaper screen module on the DIY market.