A free app for Android, by SigmaCode Tech..

MP3 Merger: Audio Joiner is a free music app for Android devices that allows you to create and edit your own MP3 songs. It supports a wide variety of audio formats such as MP3, WAV, AAC, AMR, and others. You can use it to cut and merge songs to make ringtones, alarm tones, notification tones, etc. It also has a built-in music editor that allows you to edit and trim the best parts from your songs to make a unique tone.

How to use MP3 Merger: Audio Joiner

This app is very easy to use. You just need to select the songs you want to cut or merge, select the output format, and select the volume and tone. You can choose to use the default settings or you can change the settings to customize the output song.