The “best” productivity app depends heavily on individual needs and workflow. However, here are 19 popular and highly-rated apps across various productivity categories that can significantly improve your efficiency:

Task Management & To-Do Lists:

1. Todoist: Highly customizable, with features for project management, collaboration, and prioritization.

2. Any.do: Clean interface, integrates with calendars, and offers natural language processing for task entry.

3. Microsoft To Do: Simple and intuitive, integrates well with other Microsoft services.

4. TickTick: Combines task management with habit tracking and calendar features.

Note-Taking & Organization:

5. Evernote: Versatile note-taking app with robust search functionality, web clipping, and collaboration features.

6. Notion: All-in-one workspace for note-taking, project management, wikis, and databases.

7. OneNote: Integrates well with other Microsoft products, offering note-taking, sketching, and audio recording.

8. Bear: Simple and elegant note-taking app with Markdown support and focus on writing.

Calendar & Scheduling:

9. Google Calendar: Widely used, integrates with other Google services, and offers various sharing options.

10. Fantastical: Stylish calendar app with natural language processing for event creation.

11. Calendly: Simplifies scheduling meetings and appointments by allowing others to book slots directly.

Focus & Concentration:

12. Forest: Gamifies focus by growing a virtual tree while you work; if you leave the app, the tree dies.

13. Freedom: Blocks distracting websites and apps to help you stay focused.

Reading & Research:

14. Pocket: Saves articles and web pages for later reading.

15. Instapaper: Similar to Pocket, designed for focused reading.

Other Productivity Tools:

16. Headspace/Calm: Meditation apps to reduce stress and improve focus.

17. Grammarly: Checks for grammar and spelling errors in your writing.

18. IFTTT/Zapier: Automation tools to connect different apps and automate tasks.

19. Google Keep: Simple note-taking app for quick lists, reminders, and notes.

This is not an exhaustive list. The ideal apps for you will depend on your specific needs and preferences. Try several apps to see which ones best fit your workflow and enhance your productivity. Remember to explore the free versions before committing to paid subscriptions.