People rely on off-the-shelf commercial single-user software systems in their daily lives and work to perform single-user tasks. People also need groupware systems to perform collaborative or group tasks. The goal of this thesis work is to develop innovative techniques for building computer applications that combine conventional single-user functionalities with advanced collaboration capabilities to effectively support people's individual and group work. This thesis work contributes an innovative Transparent Adaptation (TA) approach and associated supporting techniques that can be used to convert existing or new single-user applications into real-time multi-user collaborative versions without changing their source code. The transparently adapted collaborative systems not only support unconstrained collaboration and other collaboration features that were previously seen only in advanced groupware research prototypes, but also maintain the conventional functionalities and interface features that were previously seen only in commercial off-the-shelf single-user applications. Major technical contributions of the TA approach include techniques for adapting the single-user application programming interface to the data and operation models of the underlying generic collaboration technique and a generic system architecture for collaborative systems. The Operation Transformation (OT) technique has been chosen as the underlying collaboration technique for the TA approach due to its capability of supporting unconstrained collaboration and application independence. This thesis work has also made important contributions to OT by extending OT from supporting only collaborative plain text editing to supporting collaboration on complex data structures and comprehensive functionalities. To support the adaptation of complex data and operation models in a range of applications, this thesis work has contributed a package of advanced adaptation techniques for collaborative table editing and graphic object grouping. These techniques have not only increased the capability of TA, but have also advanced the state-of-the-art of collaborative editing techniques. To facilitate natural and smooth collaboration, this thesis work has contributed a multi-functional workspace awareness framework which is able to reduce the effort for developing workspace awareness features, and to be extended to support new workspace awareness features. Most importantly, this framework is able to deliver correct and precise workspace awareness information in the face of dynamic content and view changes in TA-based systems, which is an innovative feature unavailable in existing techniques. The TA approach and supporting techniques were developed and tested in the process of transparently converting two commercial off-the-shelf single-user applications - Microsoft Word and PowerPoint - into real-time collaborative applications, called CoWord and CoPowerPoint, respectively. CoWord and CoPowerPoint not only retain the functionalities and the 'look-and-feel' of their single-user counterparts, but also provide advanced multi-user collaboration capabilities for supporting multiple interaction paradigms, ranging from concurrent and free interaction to sequential and synchronized interaction, and for supporting detailed workspace awareness, including multi-user tele-pointers and radar views. The TA-based collaborative system architecture and the generic collaboration engine software component developed from this work can be reused in adapting a wide range of single-user applications.