Now it's a part of my FusionPBX fork and fusionpbx-apps repo as well.
The idea is quite simple - to manage signals from GUI in cron-like style. Not super friendly, but most of us know what cron is.
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Limitation - it will allow you to choose only from Recordings, not like tone_stream or so.
Installation:
# cd /usr/src/
# git clone https://github.com/fusionpbx/fusionpbx-apps
# cd fusionpbx-apps/
# cp -R school_bells /var/www/fusionpbx/app/
Add
* * * * * php /var/www/fusionpbx/app/school_bells/school_bells_cron.php
to your crontab
Go to GUI
Upgrades -> Schema; App Defaults; Menu Defaults; Permission Defaults
Log out and back in
Apps -> School Bells
Enjoy!