KDE Connect is an app to connect your phone and computer. It works on most OS (windows, Linux, etc.), and it works extremely well (better than the solution developed by Microsoft).

Isn't dynamic rotation built in to Android these days?

Joplin. Organise your notes into notebooks and you can also write them in markdown. You can also save your notes encrypted and syhcronise them with the cloud to have them in all of your devices. Joplin is available in all Operating Systems. Also supposts Nextcloud so it can be self-hosted!

For me

1. MiXplorer (Mix) : Clean and powerful file manager at the same time. It's easy to use for normal user and very powerful for power users.
2. Lookup Pro: Floating dictionary that can blend in to native Android context menu when highlighting words. It's similar to iOS lookup or Kindle lookup feature.
3. Maosure: Google virtual measure app that make use of ARCore library.
4. Moon+ Reader Pro: favorite ebook reader
5. Seal: Favorite youtube downloader. Unlike other YT downloader that is riddled with Ads, it FOSS app.
6. Toolwiz Photos: Best all in one photo editor for me. It's very underrated. The variety of feature it pack is u match by any photo editing apps for me. From color correction to healing and cloning tools, the fun feature that gets old very fast like face rater, face swap, pip, etc. I just noticed that it has AI painting feature too.
7. TTS Server : Azure/Ms Edge TTS ported to Android to use it as system wide TTS. It's the most natural free TTS I've ever used. It's originally Chinese only app, but I forgot where I got English version from.

Syncthing, I setup synchronisation between my PC and phone in apps that have bad built-in synchronisation or don't have it at all, e.g. for PPSSPP: I am able to have my save files for games synchronised and keep playing a videogame on phone just where I left it off on my PC

• Spectroid: what's that sound? Do I hear that faint but annoying sound or just imagine it? With spectroid you can see the sound spectrum over time.

• Nova launcher: Lets you cutomize the home screen of your phone and make it just right. I like my apps a bit closer together in five columns instead of four. Nova launcher let's me do this.

• Business calendar: it's just so much better than the default calendar, especially if you have lots of meetings and need an information dense view.

• NewPipe has made my YouTube watching experience way better; it's a standalone app with features like ad blocking, subscriptions, and downloading.
• F-Droid (particularly the Droid-ify client) is an open-source app store that generally provides quality apps.
• Obtanium has helped me stay up to date with some of my more obscure apps, which are released only on Github. Obtanium can auto-update apps from a GitHub link or similar, which makes the process way easier.
• Auxio is a pretty good music player, it's quite lightweight but it also looks good.

All of these are available on F-Droid, I find that many F-Droid apps provide a better or cleaner experience than Google Play apps.

A few of mine :

• AndOTP : A good app for OTP that actually let's you backup your keys and move them easily and securely to a new phone
• Blokada : A system wide adblocker for Android. 4000000 ads blocked so far on my phone
• YouTube Vanced: Not really a "hidden" gem but a cool app nonetheless. I wish people knew you could get an ad free YouTube experience on mobile. It also includes sponsor block so you really get straight to content. Also let's you get a YT popup player and shutdown the screen with the video still playing.
• F-Droid an Android open source app market. Often includes apps that are not allowed on Google market.

I just want to share my positive experience with Folder Sync.

I use Obsidian for journaling and note-taking, and unless you use the paid plan it doesn't have native sync across multiple devices. I have the root folder of my notes stored in Google Drive and use Folder Sync to sync my PC/laptop with my mobile. Very useful as I'm out in the field often and like to jot down quick notes on my phone.

10/10 it just works.

Any "Simple Mobile Tools" application. They are simple (obviously) and do their job well.

Keepass2Android Tasker Joplin DropSync, OneSync, DriveSync Evanova EDS Total Commander Aegis Instander Stocard Waze

I'd add Tasker to that list, even if some of the functionality requires root. It's actually insane how powerful Tasker is.

Mixplorer - aka MiX, the only file explorer I've ever needed. It's intuitive enough for basic file browsing, but it can do heavy lifting tasks. I exclusively move files on and off my phone by starting an FTP server.

Pulsar - One of the only apps I've ever paid for, it's a music player that does everything I want and nothing I don't. I'm one of those nuts who still maintains a personal library of thousands of songs rather than using spotify or whatever.

MS Swiftkey Keyboard - I went looking for this when Swype was finally discontinued. Gesture typing wasn't common yet and I still find google's stock keyboard absolutely insufferable. Swiftkey lets me adjust the size and layout of the keyboard with far less restriction.

RadarScope. I work a very weather-dependent job.

1. Copy: Allows you to copy text from apps where it usually isn't possible (eg. Instagram). While certain Pixel phones come with a similar feature in the form of OCR, it does not work with non-English text.
2. Island: Allows you to run two of the same app on a single device - for example if you have two phone numbers and want to use WhatsApp for both numbers on the same device. Some companies like Samsung and OnePlus have this functionality built-in, but they may restrict it to certain apps. Island works with all apps.
3. Unit Lab: Well designed unit converter that should honestly be a default app on all operating systems. It allows for simple unit conversion (weight, temperature, currency, length, etc.) while also allowing you mix units in calculations (eg. 5 miles + 10 km + 2650 ft).
4. RustDesk: An open source alternative to TeamViewer.

Quick Cursor: Makes it easier to use large smartphones with one hand.

+1 for Musicolet, it's fantastic.

I don't use a lot of apps I'm overly impressed with but FamilyAlbum is great if you have kids, want to share photos with family, and don't want to plaster them all over social media. You put you photos on there and give family access. No more Grandma begging for more pictures. Its not perfect. They try to get you to buy prints a lot, but otherwise a very good idea executed simply enough that the elderly can access it.

I had been using Musicolet for the longest time, switched to Vinyl Music to try to stay more FOSS.

• CPU-Z summarizes literally everything about your mobile phone. What model you have, what SoC you have, what your clock speeds and thermals are, which update you're on, etc. Super useful and you never have to wonder anything about your specs.
• Notebloc is the best camscanner app. The ads are a lot but you can get an ad-free version for pretty cheap. The black and white scan has great clarity that makes it look legit like it's scanned.
• PlainApp is a new open-source Airdroid alternative. Easily transfer files and images from your mobile to PC over wi-fi. It's super useful.

Musicolet is a great app. I've been using it for a long time.

FairEmail: I hated reading email on my phone, till I found it. I was so happy that I already paid for it 3 times (optional!) just to give something back to the dev.

Waze: it belongs to Google now, but I like it much better because it's like a social network for navigation and maps. You can also edit the maps by yourself. Another advantage is that it shows speed limits and warns you about police while driving.

aCalendar+ in combination with nextcloud. Sorted my life completly. Imo the best calender app for Android.

Image Toolbox the name explains all. Adfree ☝🏻

Paperless mobile adding documents has never been easier. Scanapp inclusive ☺️