Cronoid is the best automation tool.
It's very simple and powerful automation.

Perform task on a regular basis as cron.
It is also possible to perform tasks automatically when the state of the terminal has changed.

Easy to use.
It may only be three set of Trigger and Action and Limit.

Trigger - This is the condition that will trigger to perform the task.
Action - This is the process the contents of the task.
Limit - This is the condition in order to limit the execution of the task.

Triggers

Calendar Task
Wifi Task
External power supply Task
Calendar
Wi-fi
External power supply
Battery level
Screen light
Headset
SMS Received
App start-up
Weather forecast
Bluetooth

Actions

Alarm
Configuration changes
Application start-up
Push notification
Application stop(kill)
Still image shooting
Send mail
Change wallpaper
Recording voice
Send SMS
Switch task enable
Run shortcut
Send http request
Speech text

Limits

Time
Screen lock state

Can use all the features in the free version.
The free version allows you to create up to five tasks.