LocalSites is a replacement for Bonjour bookmarks that were removed in Safari 11.
The app shows up as an icon in the status bar (right hand side of the menu bar), with a drop down menu listing all web pages advertised in the local network via Bonjour. Selecting an item opens the web page in the default web browser.
Pressing modifier keys before opening the menu allows targeting specific browsers instead of the default browser.
The app is in the AppStore for your convenience and as a way to support its development a bit, but it is open sourced on github, so you're welcome to get it from there and also to contribute enhancements!