These audio files (Ringtone1.ogg, Ringtone2.ogg, Ringtone3.ogg) were
created by the HoloSuite project author(s).

They are released into the public domain under CC0 1.0 Universal.
You may copy, modify, distribute, and use them for any purpose,
including commercial, without asking permission or providing attribution.

https://creativecommons.org/publicdomain/zero/1.0/