Barbouri created a quad 7-segment I2C LED backpack:

Building a case for the Programmable Voltage Reference project

I put together an I2C interface board for these displays based on a design by Adafruit, using a Holtek HT16K33 RAM Mapping 16*8 LED Controller Driver chip.

A nice feature of this chip is a dimming command that provides display dimming in 1/16 increments.

Barbouri has shared the board on OSH Park:

7 Segment X4 I2C LED backpack V1.0