Ringdroid

The original open-source ringtone editor for Android, first published in 2008 and downloaded by millions of users worldwide.
Ringdroid lets you create personal ringtones, alarms, and notification sounds from existing music/audio files and record new ones using your Android device.
This app is the only 'official' distribution of the Ringdroid open-source project; it does not, and never will, contain ads.
Google Play Store automatically presents the correct Ringdroid update to install with your Android system:
Ringdroid 2.7.3 is recommended for Android system versions 4.1 ('Jelly Bean') and higher. It includes the ability to read OGG Vorbis audio files, and it saves ringtones in AAC (.m4a) format.
Ringdroid 2.6 is recommended for Android system versions 3.0 ('Honeycomb') through 4.0.3 ('Ice Cream Sandwich'). It includes user interface features such as 'pinch-to-zoom'.
Ringdroid 2.5 continues to be recommended for earlier Android system versions.
Note: this app requests access to your contacts, but solely for the purpose of setting contact-specific ringtones. Source code is available at ringdroid.com.