A free program for Android, by swengeer.
One Rep Max Calculator is among the best rep calculator app out there. With this app, you can calculate the exact number of reps you can do in a single row. This will not only help you with your workout, but also will be a great way to keep track of your progress.
You can enter the lifts you use with the Lift Name Editor.
There are also seven methods you can use for your calculations: Brzycki, Epley, Lander, Lombardi, Mayhew, Oconner, and Watham.
Additionally, this app has a record-keeping function to store your data for easy tracking. You can even have a visual presentation of your progress using graphs.