In this paper we propose a computational grid platform called JaWS++ that seeks to harvest the power of idle pools of workstations connected through the Internet and integrate them in a grid computing platform for the execution of embarrassingly parallel computations. The computations are developed in the portable Java programming language and an API is provided for application development. JaWS++ is a compromise between scavenging and reservation-based computational grids. Its service layer is composed by pools of workstations that are autonomously administered by different organizations. Each pool participates in JaWS++ under a well defined timetable to reduce unforeseen availability problems, increase dependability and favor batch work allocation and offline execution.