[The Best Apps You've Never Heard of] Sentimental Sugarcube:
I've been curious as to what apps other people know about that many others never checked out or even heard of (i.e. under 100M+ downloads), since I have my own list, too. This is the list of interesting apps I've come across:

Boost for reddit | It loads faster, doesn't crash as much, has advanced functions, and is way more customizable than the official Reddit app.

https://play.google.com/store/apps/details?id=com.rubenmayayo.reddit

CocoCam (by MagicDmStudio) | It has cute, aesthetic stickers, frames, and filters — it reminds me of PicsArt in some ways, but it's way simpler and is much more affordable.

https://play.google.com/store/apps/details?id=com.imendon.cococam

Collage Maker (by Grit Inc.) | I tested out 8 free/nearly free collage maker apps, and this one was the one — free (contains minimal ads), simple, easy to use, and is the best alternative to GridArt!

https://play.google.com/store/apps/details?id=com.binghuo.photogrid.collagemaker

Daylio Journal - Mood Tracker | It's an excellent mood, activity, habit, and pattern tracking app — it's incredibly thorough with its advanced statistics, and is very customizable.

https://play.google.com/store/apps/details?id=net.daylio

DRNK - Drinking Games | It's a completely free, fun, and customizable drinking game that features truth or dares. I've gotten hammered a dozen times playing this game with others!

https://play.google.com/store/apps/details?id=com.guillaumebadi.drnk

Flo Ovulation & Period Tracker | I honestly don't even use any of the other functions besides tracking just my period, but it's really important and I've been keeping track of it since 2017 now.

https://play.google.com/store/apps/details?id=org.iggymedia.periodtracker

GoodRx: Prescription Coupons | It brings down the cost of my medications by a highly significant percentage, and has a new feature called "GoodRx Rewards" in which you can earn points for coupons!

https://play.google.com/store/apps/details?id=com.goodrx

Google Voice | It's basically a burner number that's linked to your Google account — except, it's completely free.

https://play.google.com/store/apps/details?id=com.google.android.apps.googlevoice

Pulse Oximeter - Beat & Oxygen | It's a great substitute for Samsung Health's BPM tracker (because Samsung Health sometimes has trouble tracking very fast heart rates).

https://play.google.com/store/apps/details?id=com.dungelin.pulseoximeter

Quora — Ask Questions, Get Answers | It's somewhat different compared to other (universal) internet forums, like Reddit or 4chan — for the information I tend to read about, I'm able to find what I need on there.

https://play.google.com/store/apps/details?id=com.quora.android

TextNow: Call + Text Unlimited | It's the best burner number app, in comparison to Text Free, Burner, and Sideline, in my opinion. It does have a lot of ads, so be prepared to have an ad blocker ready.

https://play.google.com/store/apps/details?id=com.enflick.android.TextNow

Whisper | "Share confessions, thoughts, and stay anonymous (or not); see posts locally and worldwide!" The app's gone to ****, to be honest, but I'm probably always going to have a Whisper addiction.

https://play.google.com/store/apps/details?id=sh.whisper