In case you missed it, last month Microsoft released a great new feature: You can now deploy apps to mobile devices without needing the device enrolled!
To make use of this feature, your Intune tenant must be migrated to the new Azure portal experience – If you don't see the intune bits in your Azure portal, check the office365 messaging centre because it's possible your migration is blocked due to a blocking configuration and it might need some work from you to complete.
To deploy an app to the Enterprise App Store simply select an existing app in the Azure Portal (Microsoft Intune > Mobile Apps – Apps) then assign the app to an Azure AD user group as Available with or without enrollment.
Now users in that assignment group can go to https://portal.manage.microsoft.com on any of their devices and install the application without needing the device to be enrolled in Intune.
Update 19/10/2017 : Now (as of October 2017) you can optionally use the company portal app on Android to download and install your company LOB apps. The company portal app has been updated so that it wont prompt users to enroll if a LOB app is configured to not require enrollment.
User goes to https://portal.manage.microsoft.com and signs in with corporate credentials
User sees the curated list of work apps that have been published as Ávailable with or without enrolment
For apps linked to the public stores, users click "View in Store" option.
Line of business (LOB) apps that have been uploaded to the store can be installed directly.
If your testing this with a device that has been previously enrolled in MDM via the company portal app you might get an error when trying to install the app: "The device is no longer available."
All you have to do is clear the browser cookies or use in-private mode to get around this.