island is described as 'What is “Island”'. There are more than 10 alternatives to island for Android, Android Tablet, Online / Web-based, Firefox and F-Droid. The best alternative is Firefox Multi-account Containers, which is both free and Open Source. Other great apps like island are Shelter (Free, Open Source), Parallel Space (Freemium), App Cloner (Freemium) and Insular (Free, Open Source).
The Firefox Multi-Account Containers extension lets you carve out a separate box for each of your online lives – no more opening a different browser just to check your work email! Here is a quick video showing you how it works.
“Insular” is a sandbox environment to clone selected apps and isolate them from accessing your personal data outside the sandbox (including call logs, contacts, photos and etc) even if related permissions are granted. Device-bound data (SMS, IMEI and etc) is still accessible.
Easily open disposable containers that isolate attached data and are deleted after usage: Fully automatic, based on navigation-target, for certain websites, with configured mouse clicks on links or just by using the toolbar icon.
Firefox extension to automatically open websites in a container. Map multiple domains and subdomain to a container with simple CSV based config. Once mapped, this extension will always open the site in a container. This behavior is disabled in private mode.
NoxApp+ is a master of managing multiple accounts, especially designed for social apps and games. If you have more than one account for the same app, use NoxApp+ to run them simultaneously on your phone. .