Methods and systems for network-based or Internet-based software delivery are described. In one embodiment, an application program or software platform resides on a client. The program or platform is configured so that it is extensible based on software extensions that are deliverable over a network such as the Internet. In the described embodiment, extension files that comprise a software extension are hosted on an Internet server. Additional files are also hosted on the Internet server and describe aspects of the software extension. Extensions are incorporated on a client by navigating to a particular Internet site through which the extensions can be accessed. The files describing the extension files are downloaded on the client. The extension files are then downloaded and incorporated into the program or platform.