This app makes it easy for me to learn students' names, take attendance, and e-mail attendance summaries to myself in spreadsheet form. (Other export forms are also available.) It also lets me send not only e-mails but also text messages to individuals, to everyone absent on a particular day, or to all students in a class. I love being able to let students know if I'm going to be late because of a meeting I can't leave or absent because of illness.
Limitations imposed by my mobile service provider make it necessary for me to use a workaround to text everyone, but the workaround is relatively easy to set up. The software author has provided a number of useful updates in the three years I've been using the app, and he provides good support materials and responds to questions quickly. There is now a new version of the app which should be even more useful, but since I have retired, I have not tried it out.