Important: Before you Install

just:in comes as a disk image (DMG). To open the disk image the Security settings of the system must be changed.

1. Open the System Preferences.
2. Go to Security & Privacy.
3. Click on the General tab.
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4. Unlock the Preference Pane.
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5. Change the setting to Allow apps downloaded from App Store and identified developers.
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6. You can now head to the point Download & Installation below.

Further reading (external link): → macOS Sierra: Open an app from an unidentified developer