The concept has been a huge success in the 3D animation world. This is best exemplified by 3D Studio where outside programmers have added new functionality in almost every aspect of the program, from new modeling capabilities to raydiosity rendering engines. This software extensibility has spread into the Web editing world with Dreamweaver Extensions. Already over a hundred new extensions are available at the Dreamweaver Exchange . Although some are commercial extensions, most are available for free.
Membership is free.
Once the 'Extension Manager' is installed adding extensions is easy.