The growing popularity of mobile and internet-based services is increasingly changing the vision of smart homes from simple home automation to advanced ICT services which are accessible everywhere. Many small and large vendors and service providers across different industries are becoming more aware of the remarkable prospects in the smart living domain. Accordingly, several services bundled with different service platforms are emerging in the market, aiming at providing elderly-care, energy management, security or entertainment services. The overwhelming number of service platforms (mostly with proprietary standards and technologies) has made this domain even more complex and doubtful for users. While collective action between actors for developing common service platforms may solve the complexity and foster adoption of these services, the challenges of cooperation hinder many actors from joint attempts. In this paper, we study how inter-organizational cooperation for developing a common service platform for smart living services emerges. Specifically, we study the influence of platform leadership and platform openness on collective action. We do so by conducting a single case study on a unique collaborative elderly-care platform development project in Finland. The case was critical as it had all the required conditions (i.e. collective action for a common platform development project in the smart living domain) to test our propositions. The results indicate the important role of a central actor or platform leader in promoting and coordinating collaboration, even in the absence of strong interdependency in the ecosystem. We also found that most of the parties are motivated to cooperate for an open industry standard platform instead of a proprietary standard platform to allow easy integration of other services and devices to the platform. However, only under certain rules, the parties open up the business ecosystem and cooperate with new companies.