we need to design web and mobile app solution for a client. the requirements are following Application with offline capabilities, that will sync with cloud when you reconnect to the internet, but the database should be accessible while offline. Sync button is a must, client will be visiting some locations that don’t have internet access, and will require most recent data
Try Akeeba Backup.
From their site (Akeeba Solo):
One click backup That's all it takes to create a full site backup. The archive includes your database, files and the restoration script.
You can choose whether to backup only database or only files using pro version.
I believe you won't come across critical problems if you set permissions of all "cache" and "tmp" folders to 777.
The backup files can be automatically downloaded easily I guess. Hope this helps.