While writing has evolved away from the conventional method of using pens and paper in favor of digital tools (Li et al., 2019), English teachers continue to face difficulties in teaching writing. This study shows how mind-mapping and the program, Writeabout, can be merged for online writing classes in English for Specific Purposes (ESP) classrooms. It reports on a classroom-based research with a qualitative research design which includes class observations and essay analysis of first-year undergraduate students enrolled in the Railway Mechanical Technology program in Indonesia during the academic year 2020/2021. The analysis of students' essays via TOEIC-adopted writing criteria showed that the students lacked competence in vocabulary (range: 2-5), grammar (range: 2-5), and sentence quality (range: 2-5). However, their text organization skills were a bit higher (range: 3-7), which was likely due to the course instructions incorporation of mind-mapping techniques. The findings revealed that incorporating the mind-mapping technique and the Writeabout application into online writing lessons can have a positive effect on students' writing.