An emerging trend in Social Networking sites and Web portals is the opening up of their APIs to external application develop- ers. For example, the Facebook Platform, Google Gadgets and Yahoo! Widgets allow developers to design their own applications, which can then can be integrated with the platform and shared with other users. However, current APIs are targeted towards develop- ers with programming expertise and database knowledge; they are not accessible to a large class of users who do not have a programming/database background, but would nevertheless like to create new applications. To address this need, we have developed the AppForge system, which provides a WYSIWYG application development platform. Users can graphically specify the components of webpages inside a Web browser, and the corresponding database schema and application logic will be automatically generated on the fly by the system.

The WYSIWYG interface gives instantaneous feedback on what users have created and allows them to run, test and continuously refine their applications. AppForge has been used to create prototype versions of a variety of applications such as an event planning system, a recruiting system, an item trading system and an online course management system. We have also conducted a small and preliminary user study to identify and fix some of the usability aspects of AppForge.

As the world moves towards Web 2.0, there is an increasing need to leverage webpages as computing platforms that can enable users to build their own applications. For example, in Facebook and Yahoo! Groups, different groups of users have different needs, and it is difficult for these websites to build applications that satisfy all of these needs. Thus websites are starting to open up their APIs to their advanced users so that they can build new applications that can be deeply integrated with the websites, e.g., the Facebook Platform [30], Yahoo! Widgets [34] and Google Gadgets [20].

However, current APIs and tools are primarily targeted towards developers who have programming and database knowledge. Consequently, they are beyond the reach of the majority of users who lack this knowledge, but would nevertheless like to create and share their own custom applications. For instance, members of a book club in Yahoo! Groups may wish to create a custom application for managing their club events (since no third party application is available to satisfy their specific needs), but the group members may not have the necessary programming expertise to develop this application. Put another way, even though there has been a lot of work on designing languages and tools to simplify application development, ranging from high level programming languages such as Ruby on Rails [28] and Hilda [37] to visual programming tools such as Visual Basic [4] and Oracle Forms [18] to various CASE tools such as UML [7] and WebML [8], the abstractions that these tools provide is still too complex for users with limited programming and database knowledge.

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