https://www.refinerycms.com

Extendable, adaptable rewrite of django.contrib.admin

XDM: eXtendable Download Manager. Plugin based media collection manager.

Guacamole is an extendable and efficient rendering system for visualizing different data types.

Extendable vanillaJS slider

Surikat Kung-Fu - Multisite extendable version - Framework for web developers

CarbonMU is a general-purpose, extendable MUD/MUSH server written in Ruby. Not ready for public use yet.

An extendable Ruby on Rails CMS that supports Rails 3.2 and 4.0