I use the .dev domain a lot on localhost when working with Rails apps in development. It seems that the Chrome 63 update has stated enforcing HSTS on .dev domains, which means you'll need self-signed certificates for your dev environment sites to work. Mindblowing! .dev is now an official gTLD that has been bought by Google, so it might be better to switch to another gTLD for development.
Puma-dev
My favorite way of handling Rails dev environments on a local machine right now - puma-dev. A quick way to work around this, as outlined by @subvertallchris in this Github issue:
# 1. Kill your active puma-dev process
# 2. Change your gTLD of your puma-dev servers
puma-dev -install -d localhost
Now your http://awesomesite.dev
will be available on http://awesomesite.localhost
.