Future web applications will be more collaborative and will use the standard and ubiquitous Internet protocols. We have previously developed System on Mobile Devices (SyD) middleware to rapidly develop and deploy collaborative applications over heterogeneous and possibly mobile devices hosting web objects. In this paper, we present the software engineering methodology for developing SyD- enabled web applications and illustrate it through a case study on a System of Calendar application, with implementation on iPAQs and its performance metrics study. SyD-enabled web objects allow us to create a collaborative application rapidly with limited coding. In this case study, the modular software architecture allowed us to hide the inherent heterogeneity among devices, data stores, and networks by presenting a uniform and persistent object view of mobile calendar objects interacting through XML/SOAP requests and responses. The performance results we obtained show that the application scales well as we increase the group size and adapts well within the constraints of mobile devices.