Mac

Mac 64 bit, Mavericks onwards.   Version 1.0.3
Instructions: Open the DMG by double clicking on it. Drag Print42 into Applications. 

Download for Mac

Windows

Windows 10 64 bit. Latest version of Windows as of 2018. It may work with earlier versions of windows.
Version 1.0.3

Instructions: Run the setup executable.

Download for Windows

Drivers?

Print42 comes with its own driver (auto installed, so you don't need to worry).
Print42 co-exists happily with the normal Epson drivers for your Epson thermal printer.  For a list of Epson thermal printer driver downloads click here
Only registered versions actually print to a thermal printer.

You don't need to worry about drivers or hardware at all if you want to simply use Print42's free mode.
Print42 can print selections of tape to normal desktop printers, if you wish. This is free - but you want to buy a thermal printer to experience the coolness of line by line printing :-)

Note: Unregistered versions of Print42 will attempt to print a couple of lines to a thermal printer, allowing you to test any thermal printers you may already own, before purchasing a license.

Non Epson Thermal Printer? - yes you can!

I originally hardwired Print42 to be talking to Epson printers at address 0x04b8, 0x0e03 which is the VendorID, ProductID respectively.

To make things work with your non Epson printer you need to find out VendorID, ProductID for your printer and put that information in the Print42 config file. If you are on Mac, there is a utility called lsusb which lists your devices and their addresses - really handy.  You can install it on Mac using a terminal, as long as you have the Brew tool installed type brew install lsusb and then type lsusb and see if you can see your printer listed. If on Windows, USBDeview might work, otherwise there are some options discussed here.

Once you have your printer's VendorID, ProductID which might look something like e.g. USB\VID_B000&PID_0410 (just take the bold bits, the numbers in hex) all you need to do is add 

"vendorid": "B000", "productid": "0410"

to the JSON preferences file which is located at:

~/Library/Application\ Support/Print42/prefs.json   (Mac)
C:\Users\YOURNAME\AppData\Local\Wware\Print42\prefs.json    (Windows)

and be running version 1.0.3 or higher of Print42. You can check the logs of the last few runs from the Print42 help menu and see if the correct address of the printer is there OK. The relevant log entries should be near the bottom of that log window. Ensure your editing of the json is valid JSON, which you can check by copying the entire contents of that file and using an online JSON format checker