aCalendar

Google Tasks Sync

aCalendar syncs directly with Google Tasks. It uses your Android system account for safe login, so you never have to enter your Google password in aCalendar (you only need to give permission to manage tasks).

Limitations: Google does not offer timed tasks or repeating tasks in its developer interface (API) yet, so these Google features cannot sync with aCalendar.

Google Keep & Google Reminders

Google Keep and Google Reminders cannot be synced to aCalendar because Google does not provide a public developer interface for them.