Adaxes is a standalone software solution that acts as a proxy between users and your on-premises AD, Azure AD, Exchange, and Microsoft 365.
Adaxes does not pollute your on-premises AD or Azure AD in any way. It doesn't store any of its data in your directory, doesn't change native permissions, and doesn't extend the schema.
Adaxes can manage as many domains as you need. Both, on-premises AD and Azure AD domains are supported. In fact, Adaxes blurs the line between on-prem AD and Azure AD.
You can set up multiple Adaxes service instances that share common configuration. This enables you to distribute the load across multiple servers and provides a failsafe mechanism.