Using wp single login you can easily add the functionality to allow only single login per user.
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ACF Field For CF7
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Sky Login Redirect
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Lazy Loader
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PiWeb Export Customers Users & Guest customer to CSV for WooCommerce
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Muki Floating TOC
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AP HoneyPot WordPress Plugin
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SV Tracking Manager
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Event Genius – Event Management, Registration, RSVP, and Tickets
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WP Activity Log
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Force Regenerate Thumbnails
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First payment date for WooCommerce Subscriptions
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Colorize Mobile Browser Address bar
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One User Avatar | User Profile Picture
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Admin Menu in Frontend
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WP Subdomains (Revisited)
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Blogger Importer Extended
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Page-list
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Timologia for WooCommerce