In the last 15 years, European countries have invested considerable resources to provide e-government services. Despite of its increasing availability, its level of adoption has not been satisfying. On the other hand, over the last years, coinciding with the web 2.0 trend, the e-government services co-produced by citizens start to appear, often without the support, acknowledgement and even awareness of the government. This trend stems from a well-established tradition of offline co- production of public services, i.e. services provided by the voluntary sector, but brought to an unprecedented scale thanks to the advent of web 2.0. Still, the concept remains not well-defined and its impact is not yet well studied. The paper explores on a limited sets of cases what does it mean to collaboratively deliver online public services; what are the success factors based on the cases under study and what are the incentives for service providers (other than public administration), citizens as users and public administration. The authors propose an ostensive definition of the collaborative delivery of public services: collaborative public services are created and run by government, civil society or by private sector building on the re-use of government data or citizens data. Those services are focused on public goods delivery (e.g. health, education, public transport) and are meant to change the traditional government services by engaging in an open dialogue with public administration about the best way to deliver those services. The analysis of six case studies of innovative collaborative online public services suggests that the online collaborative public service delivery increases its quality with the users׳ growth contrary to the traditional offline service delivery. The study results indicate that the current developers interest lies in delivering complementary services to the government run services rather than substitutive services. The authors propose also the initial list of success factors, enabling conditions, and benefits for all main stakeholders (users, innovators and public administration).