This document introduces AcaWriter, an open-source learning analytics tool that provides automated formative feedback on students' academic writing. It analyzes texts to identify rhetorical moves using natural language processing techniques. The tool is grounded in genre theory and aims to help students learn discipline-specific writing conventions. Three implementations of AcaWriter are described where it was customized for different learning contexts and evaluated. Overall, AcaWriter shows potential for improving writing skills through personalized, scalable feedback.