v3.0 - Umbraco dotnetCore release
With most of the work being done by @AaronSadlerUK - we have a donetCore version of Maintenance Manager 🎉 .
Maintenance Page
This version uses middleware to intercept requests and turn off the site which is better than before because we no longer rely on you having not swapped out your default render controllers.
You can quickly set things like text, notes and titles in the settings and the "maintence template" is also delivered from a RazorClassLibrary which means it doesn't clutter up your views folder (unless you want it to, in which case you can create your own maintenance template and use that in its place).
BackOffice restricted access,
there is also an option that lets anyone who is currently logged into the back office past the maintenance mode page, to see the site, so your site can be publicly locked while still available to logged in people.
Content Freeze
You can also choose to freeze your sites content (you don't have to also be in maintenance mode to do this!) - which will stop any back office users from editing things on the site while you do the upgrades etc you need to perform.
Installing
via dotnet
dotnet add package Our.Umbraco.MaintenanceMode