If you go onto the Chrome Web Store, there is a section for Apps. These can be standalone "applications" on your computer that can run without Chrome being open. If you want to test this out to see what I'm talking about, try installing the app version of Google Keep or Google Hangouts. On your Chrome Apps screen (type chrome://apps/ in your address bar if you can't find this), you can right click one of them and select "Create Shortcut". Now you have a "desktop application" that can run separately from chrome.
Join should have an app-version on the chrome web store. I would love to keep a window of Join open for SMS and notifications without having to keep Chrome open.