I'm on the lookout for categories of apps that "print" money for their makers and represent a potential opportunity for developers who want to get into proven niches.

A few weeks ago I uncovered identifier apps and this week I found a new category: Storage cleaners.

According to data from Appfigures Explorer, consumers spent nearly $40M on storage cleaner apps in the last month. Much more than I'd expected.

There are a little over 1,500 storage cleaning apps across the App Store and Google Play, and all revolve around organizing/deduplicating/compressing photos. Some offer additional "cleaning" features like compressing videos, and others offer miscellaneous features like built-in ad blockers. But the main goal is to remove unnecessary photos to save space.

A feature Apple can easily sherlock next week. But it probably won't.

Here's what's interesting, more than half of all apps and more than 95% of the revenue is on the App Store. While there are a few hundred apps on Google Play most don't generate much revenue.

That's because most Android devices come with some of these features built in, making it a great opportunity for iOS developers.

We've seen this before with QR code scanners, which are built into Android and not iOS (well, at least), and are generating millions on the App Store.

Available natively on Android but not on iOS = opportunity.

Money Please

How big is this opportunity? Our App Intelligence shows 161 cleaner apps grossed at least $1,000 last month, 42 more than $100K, and 7 more than $1M.

There's a ton of competition, but because there's very little brand affinity in this category and most icons looking fairly identical, users will download what they see first, and there are quite a few ways for developers to achieve that.

I analyzed the top earners on the App Store, which include: Cleanup, Cleaner Guru, AI Cleaner, Cleaner Kit, Swipewipe, Phone Cleaner, Powerful Cleaner, Cleanup App, Cleaner, and Cleaner AI.

We estimate that the group grossed $197M in 2024 and is on track to double that in 2025 having already earned more than half in the first five months of the year and growing rapidly.

Organic Or Paid?

I looked into how these apps are promoting themselves within the App Store to see if App Store Optimization or Apple Ads are required to succeed, and based on the data the clear answer is both.

The top 10 earners run Apple Ads campaigns with thousands of keywords in the US, where the majority of revenue is coming from. But that's not it, each is also ranked in thousands of keywords organically. Looking at their names it's clear that's not by accident.

Should you build a storage cleaning app? Maybe! The niche is very competitive and already has one clear leader, but lots of competitors are still making money. The key to building for a niche isn't necessarily following the hottest trend but rather finding the right niche.

Have you ever heard of NotebookLM? If you haven't, NotebookLM is an AI tool from Google that turns written documents into realistic sounding podcasts.

Too good to be true? Not really! I tried it and was pleasantly surprised.

NotebookLM was web only since its release, but last month, Google quietly released a mobile app.

And people noticed!

According to Appfigures intelligence, NotebookLM crossed 1M downloads within 10 days of its release and at this point is already on 1.3M devices.

That's fairly similar to Meta's new AI app which got a lot more coverage than NotebookLM.

Downloads were pretty balanced between the App Store and Google Play, and the US was the biggest driver of downloads across both with Japan in second place on the App Store and India in second place on Google Play.

Unlike ChatGPT, Grok, DeepSeek, Claude, and other AI apps, NotebookLM sits in a category of its own. But Grok has been pushing its voice model more and Claude just got into that race as well so I expect to see more competition in this space.

Beyond competition, what I'm more interested in seeing is how this technology will be used in the wild. Google hasn't put an explicit policy (that I could find) on NotebookLM's output, but I see quite a few clever ways to use it to describe content in a knowledgebase, read technical articles, and more.

If that does catch on, it'll be Google's game to lose.

If you make a better app, more people will want it, right? Well, that's something Nintendo seems to have taken seriously with its revamped companion app for the newly launched Switch 2 console. And it worked!

Originally launched in 2017 as the Nintendo Switch Online app alongside Splatoon 2, the app enabled voice chat but was clunky and rarely used. Despite that, Appfigures intelligence shows it amassed 39M downloads over time, largely thanks to holiday spikes when new consoles were gifted.

But that's changing.

Nintendo announced that voice and video chat would be integrated into the Switch 2's OS, accessible via a dedicated controller button. The app itself would be overhauled and renamed simply Nintendo Switch in time for the new console's release, but with key additions including automatic screenshot uploads, friend status and play history tracking, and sidekick features for titles like The Legend of Zelda: Breath of the Wild and Tears of the Kingdom.

The refreshed app debuted in late May and hit 15K downloads in one day, up from a daily average of just a few thousand. With the Switch 2 now out, adoption is accelerating: on June 5th, the app saw 49K downloads, a 277% increase from the day prior. Over the seven days leading up to launch, it was downloaded 123K times, up 116% from the previous week.

The spike reflects not just added features but growing hype for the Switch 2 itself, which appears to be off to a strong start. Prior hardware updates like the Switch Lite and OLED drove some increased interest, but nothing on this scale!

In fact, June 5 saw more downloads than Christmas Day in seven of the past eight years.

In Japan, the app rose to #77 overall in the App Store after being unranked the week before. In the U.S., it reached #188 overall and #20 in the Entertainment category. In Japan's Entertainment category, it climbed to #10.

Also benefiting from launch-week attention: Nintendo Music, a companion app for Switch Online subscribers that streams game soundtracks. On launch day, it saw a 148% bump, about 2.5x higher, bringing its estimated iOS total to 1.5M downloads.

Did you get a Switch 2?

May is officially behind us and summer is right around the corner, and I couldn't wait any longer to rank the most downloaded apps in the world and see if the trend I've been following for over a year now continues.

And I have good news! But let's start with the winners.

ChatGPT was the most downloaded mobile app in the world in May for the second month in a row. Appfigures intelligence estimates show the AI king made its way into 50M devices in May, which is a couple millions shy of April but with enough to have the lead.

According to our estimates, Instagram made its way into 42M devices in May. A tiny bit more than April and enough to pull it into 2nd place after ranking 3rd in April.

TikTok came in third with 40M estimated downloads. A teeny tiny bit more than April, but more is always better so there's nothing to complain about here.

Other than the InstaTok shuffle, the remainder of the list is consistent with April's with Facebook and WhatsApp rounding out the top 5 most downloaded apps. Both grew a few million downloads as well.

I find it interesting that only two apps on this list aren't for chatting (Temu and CapCut).

Together, the top 10 most downloaded apps made their way into 313M devices according to our estimates. Just 4% more than April, but bucking the downloads down trend which is a welcome change as we head into the summer.

I crunched the numbers and ranked the highest-earning mobile apps in the world in May and found exactly one winner in an otherwise uneventful list.

Oh, month-over-month revenue also grew a whopping 17%! More on that later.

TikTok continued to be the highest-earning mobile app in the world in May. Not just retaining its position but also growing the gap with net revenue rising to $380M in May, according to our App Intelligence.

That's more than $51M of new revenue in May.

YouTube, which is usually the second in command on our list wasn't the second highest-earner in May. That title goes to ChatGPT for the second month in a row.

The AI king leaped into second place in April and maintained its position with $180M of estimated net revenue, what OpenAI gets to keep after giving Apple and Google their share.

Zooming in a bit, we see that ChatGPT's rank rose within our store lists across the App Store and Google Play where it's now ranked 2nd and 6th, respectively.

It's worth noting that this haul marks a 22% increase from April, which is a big deal considering the competitive landscape continues to grow rapidly.

Side note: I looked at the day-of-week revenue for ChatGPT over time and can clearly see it's moving from mid-week (business users) to end of week (broader consumer market). You'll be able to see that in Appfigures soon.

YouTube came in 3rd with $142M of net revenue, roughly 8% higher than April, according to our estimates.

Tinder and Disney+ round out the top 5 earners, and if you're keeping track, the list is identical to April's but with noticeably higher revenue.

Appfigures Intelligence shows that together, the top 10 highest earners brought in $1.4B in May marking a 17% month-over-month increase and reinforcing the trend: downloads are down while revenue is up.

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