Pretty simple; butler allows you to specify prerequisites for your game (c++ redistributable for instance) and these are installed by the itch app.  My question is: What happens outside the usage of the itch app, for instance if a user elects to download just the .zip file of a release? It seems that there is no way for the prerequisite to be installed in this instance... What is the standard procedure or usual approach to ensuring a user that downloads the .zip will be able to run the game?

When people download your game from the browser they get exactly what you uploaded. We have the "install instructions" field on your game page to give people instructions on installation, you could list the requirements there. One relatively simple thing we could do in the future is extract the list of prerequisites and generate some install instructions to go along with your page with links to the relevant things.

Ok, that makes the current expected behaviour clear. I'll manually add in the vcredist to my package and fill out the install instructions field.

FWIW I like the idea about automatically including prerequisites and generating a description for the install instructions field. I can't see a way of integrating prerequisites with just a zip download so automatic handling would be the next best thing from my perspective.

EDIT:

Haha looks like the 'install instructions' has specific language in the description indicating that steps for installing prerequisites should be included there, guess I missed that :P