Buildings, with their different subsystems interacting with diverse occupants, constitute a complex Cyber-Physical-Human infrastructure. Monitoring and controlling this complex ecosystem is essential both for efficient and optimized operations of building subsystems and for influencing the occupant behavior. A critical enabling technology in this case is a middleware system for buildings that can provide support for deriving rich inferences by fusing and analyzing intentionally acquired or opportunistically available data from diverse embedded sensors, human feedback, and existing building subsystems. This paper presents Sensor Act, a Scriptable middleware system architecture for energy management applications in buildings. In addition to providing support for managing and integrating heterogeneous sensing and actuation systems in buildings, Sensor Act provides two emerging features: (1) a scripting framework for application developers to extend and automate the various energy management functions of the buildings, and (2) a rule-based sensor data and control sharing mechanism for fine-grained sharing for building owners. We describe the detailed system architecture and design, and provide proof of concept through multiple third party applications built using Sensor Act APIs and deployment in diverse settings across India and United States. Sensor Act is released in open source for community use.