TTyGO is a simple VT220 compatible serial terminal with some XTerm extensions with optional UTF-8 support. Hardware buttons act as VT220 programmable function keys, and there is an on screen keyboard available.
It uses the U8g2lib graphical library, so it is compatible with a lot of displays.
TTGO OLED ESP8622 SH1106
Either either the serial-over-usb connection, or the physical TTL level serial port can be used. Maximum serial speed is 115200baud and maximum screen size is 24x12 characters. 3 physical buttons leading to 6 (or 5 with the on screen keyboard enabled) programmable functions. All software features can be enabled.
Arduboy (Production version)
Maximum serial speed is 9600baud and maximum screen size is 24x12 characters. 6 physical buttons leading to 12 (or 11 with the on screen keyboard enabled) programmable functions. Software features are limited by available memory - in particular there is no unicode support.