Google calendar

Simple Calendar – Google Calendar Plugin

Calendar

Backup

https://wordpress.org/plugins/dropbox-backup/ – seems to be free

https://wordpress.org/plugins/wp-backitup/

https://wordpress.org/plugins/updraftplus/ – free and paid (over 900k installs)

https://wordpress.org/plugins/wordpress-backup-to-dropbox/ – free and paid features

BackWPup – WordPress Backup Plugin