This article presents a rule-based agent mechanism as the kernel of a ubiquitous end-user, UI–independent programming system. The underlying goal of our work is to allow end–users to control and program their environments in a uniform, application-independent way. The heterogeneity of environments, users and programming skills, as well as the coexistence of different users and domains of automation in the same environment are some of the main challenges analyzed. For doing so, we present our system and describe some of the real–environments, user studies and experiences we have had in the development process.