As of my last knowledge update in September 2021, I can’t provide you with information about specific apps or “unknown gems” on the Google Play Store that might have gained popularity after that date. However, I can suggest some types of apps that are often overlooked but can be quite useful or entertaining:

1. Productivity Apps:
   • TickTick: A task management app that offers a range of features to help you stay organized.
   • Notion: An all-in-one workspace for note-taking, task management, and collaborative work.
2. Health and Wellness:
   • Insight Timer: A meditation and sleep app that offers a variety of guided sessions and relaxation techniques.
   • MyFitnessPal: A comprehensive app for tracking your diet and exercise routines.

1. Creativity and Learning:
   • Elevate: An app that provides personalized brain training games to improve cognitive skills.
   • Duolingo: A language learning app that offers interactive lessons for numerous languages.
2. Entertainment:
   • Pocket Casts: A podcast app that offers a user-friendly interface and useful features for podcast enthusiasts.
   • Shazam: An app that identifies songs by listening to a short sample of the music.
3. Customization:
   • KWGT: A widget maker that allows you to create custom widgets for your home screen.
   • Nova Launcher: A highly customizable launcher that lets you personalize your Android device’s look and feel.
4. Reading and News:
   • Feedly: An RSS reader that helps you stay updated with your favorite websites and blogs.
   • Pocket: An app that lets you save articles and web pages to read later, even offline.

Remember that app popularity can change rapidly, and new apps are released all the time. To discover the latest “unknown gems,” consider checking app review websites, online forums, and social media groups where users often share their favorite discoveries. Additionally, exploring categories in the Play Store and trying out apps with positive reviews and high ratings can lead you to some hidden treasures.