It's not new to wrap a web service such as Gmail in a standalone browser window to create a desktop app.
I don't really see the point in this however, because tabbed browsing makes it easy to switch between sites and services, even if more than one browser is required.
Rambox takes it to a higher level by specialising in email and messaging sites.
It's effectively a front-end aggregator for all your online communications.
This is particularly useful if you have multiple accounts and want to be "on call" with each of them.
There are more than 70 services which can be deployed by point and click (with user name and password), but others can be easily added.
I currently have Rambox open with Office 365 mail, Google Hangouts, Skype, Facebook Messenger, Zoho Mail, Yahoo Mail and Messenger, my work webmail and Twitter (Tweet Deck).
Notifications include sound and numeric icons for the number of messages.
All of these are aggregated in one app instead of opening individual browser tabs and/or programs.
I'm running the 64-bit Debian version on Linux Mint. Rambox also has downloads for Windows, Mac and other Linux flavors.
A convenient feature is cross-platform synchronisation, which means you can use the service on different computers with a single log-in.
It's also possible to set a master password for extra security.
The developers say no personal information is stored because sessions persist using the "partition:persist attribute for web-views".
Rambox is maintained by Argentine developers who welcome and deserve donations.