A small step up from fluid
For a long time I have created my own “apps” using Fluidapp which basically turns a webapp into a mac app. This app seems to be exactly that, with a few customizations to make it more specific to Inbox. I found it to be ok, but have switched back to airmail which is a fully fledged app, rather than a wrapper around with website. I found boxy to buggy at the mercy of frequent changes made by Inbox. Every time the site changed, it would cause different problems to spring up in Boxy which exposes the flawed design of this app. There’s no way Boxy could ever keep up with the changes in Inbox.
dstimp about
Boxy for "Inbox by Gmail"