1. Library Genesis (LibGen)

• What It Is: A digital library that offers access to millions of books and academic papers.
• Why It Feels Secret: It provides free access to academic papers and textbooks that would otherwise be behind paywalls. Legal status can be a gray area, so use it responsibly.

2. The Wayback Machine

• What It Is: A digital archive of the web, allowing you to view old versions of websites.
• Why It Feels Secret: You can dig into the history of the internet and view content that has long been deleted or altered.

3. Unroll.Me

• What It Is: A service that helps you unsubscribe from email lists and organize your inbox.
• Why It Feels Secret: It’s a quick way to declutter your inbox, but not everyone knows about it.

4. JustWatch

• What It Is: A streaming search engine that helps you find where movies and TV shows are available online.
• Why It Feels Secret: It aggregates streaming services and shows availability across platforms, which isn’t commonly known.

5. 10 Minute Mail

• What It Is: A disposable email service that provides a temporary email address.
• Why It Feels Secret: Useful for signing up for services without giving out your real email, which feels a bit sneaky.

6. PDF Drive

• What It Is: A search engine for free PDF books.
• Why It Feels Secret: Provides access to a large collection of books in PDF format, sometimes including copyrighted material, so tread carefully.

7. Have I Been Pwned

• What It Is: A site that lets you check if your email or phone number has been part of a data breach.
• Why It Feels Secret: Offers a glimpse into the dark side of the web, showing where your personal information might have been exposed.

8. GeoGuessr

• What It Is: A geography game that places you somewhere in the world in Google Street View, and you have to guess where you are.
• Why It Feels Secret: It’s an addictive game that feels like you’re exploring hidden corners of the globe.

9. Radio Garden

• What It Is: Lets you listen to radio stations from around the world by rotating a globe.
• Why It Feels Secret: It gives you a direct window into the culture and music of places you might never visit.

10. FutureMe

• What It Is: Allows you to send an email to your future self.
• Why It Feels Secret: It feels almost mystical, writing a letter to yourself and not knowing how things will change by the time you receive it.

11. FlightRadar24

• What It Is: Real-time tracking of aircraft flying over the world.
• Why It Feels Secret: Gives you the ability to track specific flights and aircraft, something that feels like insider knowledge.

12. This Person Does Not Exist

• What It Is: AI-generated faces of people who don’t actually exist.
• Why It Feels Secret: The concept of creating lifelike faces from scratch feels like something out of a sci-fi movie.

13. Sleepyti.me

• What It Is: Calculates the best time to go to bed or wake up based on sleep cycles.
• Why It Feels Secret: Helps optimize your sleep without needing any fancy apps or gadgets.

These websites are interesting, useful, and might give off a “secret” vibe due to their specialized functions or low public profile. However, always ensure that your usage is within legal and ethical boundaries.