Question: I'm looking for a scalable authentication system that can handle multiple organizations and users with ease.

If you need an authentication system that can grow with you to accommodate multiple organizations and users, PropelAuth is definitely worth a look. It's a full-featured multi-tenant authentication and authorization service that includes features like organizations with self-service UIs, SAML support, roles/RBAC, multiple sign-in methods, and customizable security settings. The service is geared for B2B products, so companies of any size can focus on their main product while delivering a good user experience.

Another good option is Clerk, a full-stack user management platform that handles authentication and user management for your apps. It supports multifactor authentication, advanced security and multiple login mechanisms, and has features for multi-tenancy including custom roles, auto-join and organization UI components. Clerk also has a free tier for up to 10,000 monthly active users and 100 monthly active orgs, so it's a good option if you're looking for something that's easy on the wallet.

Auth0 is a mature authentication and authorization service that works with many languages and frameworks. It offers Universal Login, Single Sign On, Multifactor Authentication, and passwordless options, among other features. Auth0 can handle small startups and large enterprises, and it's free to try out and evaluate.

Last, LoginRadius offers a user identity management platform that's designed to simplify authentication and single sign-on across multiple applications. It includes advanced login mechanisms, cloud-based directory services and powerful user management features. With a cloud-native architecture and flexible deployment options, LoginRadius is designed to scale and handle large volumes of user traffic.