All of the required components are surface mount to easily fit into a wallet for use as a business card.

This sounds terribly difficult if you have never tried soldering surface mount components before but it is incredibly simple, no need to use your iron.  Get some low temp solder paste and any cheap hot air gun will work(preferably temp controlled hot air rework station), but even a frying pan or hot plate will work.  Just dab, place, and heat, then clean it up a bit when it cools.  Done...

(Any of my assembled boards already have the bootloader burned in)

Fuse: avrdude -c buspirate -P /dev/ttyUSB1 -p attiny85 -U lfuse:w:0xe1:m -U hfuse:w:0xdd:m -U efuse:w:0xfe:m -B 20

Burn Bootloader: avrdude -c buspirate -P /dev/ttyUSB1 -p attiny85 -U flash:w:bootloader.hex:i -B 20

The Micronucleus build included has a custom 1 second programming delay before running the application.   The default 6 second delay was too long to wait to run the application for my specific use case.

File - Preferences - Additional Board Manager URLs

http://digistump.com/package_digistump_index.json

OK

Tools - Board - Boards Manager... - Digistump AVR Boards - Install

Select - Board: Digispark (Default - 16.5mhz)   Programmer: Micronucleus

Upload

Jumpers

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Cut J1 to disable the capacitive touch sensor.

Cut J2 to disable R5 resistor from RST to VCC.

Bridge J3 to enter programming mode when flashed with a different Micronucleus build.    

Optional Features

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Reset Switch

Power LED - Requires 1K Resistor

Utilizing the Prototyping Area

Flashing a new application via USB

Flashing via the AVR ISP header(Do not connect a programmer while connected to a USB port)   

Notes

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The board thickness is 1.6mm and requires a shim to fit snugly into the USB port.   Currently a blank PVC ID card is cut to size and bonded using Loctite 495 Instant Adhesive. This has proven so far to be a fast, strong, and relatively consistent solution.  

Enjoy!