A free program for Android, by Sparkling Apps.

This tool allows you to make unlimited recordings of your conversations, including with your family, friends, and your colleagues. It works on all Android devices and works on most phones made by other manufacturers as well. It can be used to make high-quality audio recordings of your conversations with other people, even if they are on another phone or even if you are using a Voice Over Internet Protocol (VoIP) service.

You can record as many conversations as you want, and they will all be saved in the same folder. You can even choose to save them in a different folder.

It is a very simple tool that does not need to be used by experts.