A free program for Android, by Cyclosis.

Ringtone Maker Studio is a music editing app that lets you easily create your own ringtone, notification tone, and alarm from any WAV, AAC, MP4, or MP3 file. It also provides an easy way to preview the resulting tone, so you can make sure it’s the right sound for your phone.

The main interface is very easy to use, and you can add your favorite songs and then modify them to make them the way you want. You can cut the best part of the song and save it as your ringtone, notification tone, and alarm tone. You can also choose to save the edited version of the song as a separate file.