The World Wide Web is evolving towards a very large distributed platform allowing ubiquitous access to a wide range of Web applications with minimal delay and no installation required. Such Web applications range from having users undertake simple tasks, such as filling a form, to more complex tasks including collaborative work, project management, and more generally, creating, consulting, annotating, and sharing Web content. However, users are lacking a simple but yet powerful mechanism to compose Web applications, similarly to what desktop environments allowed for decades using the file explorer paradigm and the desktop metaphor. Attempts have been made to adapt the desktop metaphor to the Web environment giving birth to Webtops (Web desktops). It essentially consisted of embedding a desktop environment in a Web browser and provide access to various Web applications within the same User Interface. However, those attempts did not take into consideration to the radical differences between Web and desktop environments and applications. In this work, we introduce a new approach for Web application composition based on the mindmap metaphor. It allows browsing artifacts (Web resources) and enabling user-driven composition of their associated Web applications. Essentially, a mindmap is a graph of widgets representing artifacts created or used by Web applications and allow to list and launch all possible Web applications associated to each artifact. A tool has been developed to experiment the new metaphor and is provided as a service to be embedded in Web applications via a Web browser's plug-in. We demonstrate in this paper three case studies regarding the DBLP Web site, Wikipedia and Google Picasa Web applications.