What Are Your Favorite Hidden Gem Android Apps?

I'm sure there are countless apps out there that are incredibly cool, interesting, or useful, but just haven't hit the mainstream yet. Maybe it's a productivity tool that's boosted your efficiency, a unique game that's kept you entertained for hours, or a niche app that's catered perfectly to one of your hobbies or interests.

What are some Android hidden gem apps that you've used a bunch or think it's really cool/interesting/useful?

Please share your recommendations, and if possible, a brief description of what the app does and why you find it so valuable.

Looking forward to uncovering some hidden treasures in the Android app world. Thanks in advance for your suggestions!