supercharging the z80

The Hitachi HD64180 "Super Z80"
beat Zilog's z800 to market with a highly expanded, faster and more integrated z80 core.
That is why the HD64180 was chosen for the Circuit Cellar SB180, SB180FX single-board computer

Byte Magazine cover story: September/October 1985
designed by Steve Ciarcia
manufactured by Micromint
ran Z-System, an enhanced replacement for the CP/M operating system

The Rabbit Semiconductor (now digi) Rabbit 2000, 3000, 3000A extends the z80 even more.

Zilog's

z800
z180 to 33 MHz
z280
eZ80 (up to 50 MHz)

The eZ80: could've be the next 'Arduino' for IoT
with internal Ethernet and lotsa memory
but it was too little too late and poorly supported.
The yahoo eZ80 support group listed SO MANY BUG REPORTS that Zilog never fixed/patched.

48 MHz eZ80 Acclaim! module