Ultimate Multisite

An open-source WordPress plugin that turns Multisite into a Website-as-a-Service platform

Ultimate MultisiteCheck Ultimate Multisite

Best for: WordPress professionals who want to launch a site-building SaaS business (like a mini Wix) on top of WordPress Multisite.
Skip if: You're not building a WordPress-based site-builder business, or you need a more modern non-PHP stack.

Ultimate Multisite is a free, open-source WordPress plugin that converts a WordPress Multisite install into a WaaS business, similar to Wix or WordPress.com. It provides subscription management, built-in PayPal and Stripe billing, pre-designed site templates for signup, custom domain mapping, trial periods, and a coupon system, with premium add-ons available for $349.

Pros

Core plugin is free and open source, available on WordPress.org
Built-in PayPal and Stripe billing with trials and coupons
Domain mapping lets customers use their own custom domains
Supports major managed WordPress hosts (WP Engine, Cloudways, RunCloud, etc.)

Cons

Full functionality requires premium add-ons ($349) beyond the free core plugin
Tied specifically to WordPress Multisite, a more complex and less common WordPress setup
WaaS platforms built this way require ongoing operational overhead (support, uptime) not solved by the plugin itself