Elgg

Elgg is an open source rapid development framework and CMS for building socially aware web applications. It gives social apps the user accounts, groups, content, and access control they need in one PHP and MySQL stack, with a modular design that developers extend instead of starting from scratch.

A pluggable system of events, views, and auth modules lets plugins reshape core behavior, presentation, and authentication. The platform includes a flexible entity system, a file storage API, on-site and email notifications, a client-side API with a built-in Ajax service, and RPC web services for external apps. Security comes from anti-CSRF validation, strict XSS filters, HMAC signatures, and modern password hashing.

Elgg is governed by the Elgg Foundation, a nonprofit set up to maintain the project independently. It runs on NGINX or Apache, draws on a catalog of over 1,000 community plugins, and is released under the GPL v2 and MIT-X11 licenses for self-hosted PHP and MySQL deployments.