The HiSense A6 is a dual-screen smartphone that features a 6.1" 2160×1080 AMOLED display on the front and a 5.6" touch E Ink Carta HD screen on the back. Other features include a snapdragon 660 chip-set, 6 GB of RAM, 64/128 GB of storage and a dual-sensor 12Mp camera. The E Ink display can mirror the front display, which can then be used to run an e-reader application or any other application.
The HiSense A6 will ship by the end of 2019 for around $250. Here's a nice video review of this phone.