These are some of the apps I love and use on a daily basis.
1. Focus Keeper: It's based on Pomodoro technique spending 25minutes on a task then take a short break before starting another 25 minutes. This is great for managing distractions, eliminate burnout, and promote better productivity.

2. Binaural: Simple app which has multiple frequency selections to listen to when you are doing high level task, meditation, and even sleeping. Be sure to switch to airplane more when using it before bed to avoid any interruption to our circadian rhythm.

3. Any.do: I use it daily for my to-do-list and reminder. Simple and straight forward to use.