The increasing pervasiveness of urban systems and networks utilizing digital technologies for their operation generates enormous amounts of digital traces capable of reflecting in real-time how people make use of space and infrastructures in the city. This is not only transforming how we study, design, and manage cities but opens up new possibilities for tools that give people access to up-to-date information about urban dynamics, allowing them to take decisions that are more in sync with their environment. This paper documents the ongoing LIVE Singapore! project which explores the development of an open platform for the collection, elaboration and distribution of a large and growing number of different kinds of real-time data that originate in a city. Inspired by recent data.gov initiatives, the platform is structured to become itself a tool for developer communities, allowing them to analyze data and write applications that create links between a city's different real-time data streams, offering new insights and services to citizens. Being a compact island based city-state metropolis, Singapore offers a unique context for this study. This paper addresses the value of stream data for city planning and management as well as modalities to give citizens meaningful access to large amounts of data capable of informing their decisions. We describe the technology context within which this project is framed, illustrate the requirements and the architecture of the open real-time data platform to serve as a base for programming the city, and finally we present and discuss the first platform prototype (using real-world data from operators of cellphone networks, taxi fleet, public transport, sea port, airport, and others). Based on this prototype a public showcasing of the project was staged in April 2011 at the Singapore Art Museum and the visual data analytics generated are illustrated in the paper. Finally, we draw some conclusions of technical as well as organizational nature regarding the challenges we faced when working in new ways with real-world, real-time data streams in an urban context that will help inform further development of our as well as of related projects in progressing in disclosing the potential of the wealth of digital data generated by urban systems, networks, and infrastructures.