You can write native code in Go for Android and iOS.
Blokada is an ad and surveillance blocker for Android. Sets up a virtual VPN connection (so it doesn't need root) and filters all outbound connection requests. Works at the OS level so you don't have to plug it into a bunch of your apps.
Github: https://github.com/blokadaorg/blokada
F-Droid: https://f-droid.org/packages/org.blokada.alarm/
Homepage for a mobile application that lets you map to and validate Open Streetmaps satellite imint. Part of the Humanitarian Open Streetmap project.
A toolset for taking apart Android .apk files so that the binaries can be reverse engineered or modified.
The Guardian Project has released the F-Droid Repository, a catalogue of F/OSS apps for Android. Their app makes it easy to browse the repository and install the listed software on your Android device.
Note: The "Allow install from non-market sources" option needs to be checked on your Android device.
A massive list of free-as-in-beer ebooks about programming: Languages, platforms, tools, and more. Ideal for teaching classes, continuing education, reference, and getting a jump start on programming in school.
Pixitracker is a simple, pixel-based sample editor and chiptune tracker that's designed to be fun to play with, so it doesn't have the hardcore (and intimidating, I'll admit) tracker interface. Pixel-based means that you specify notes and patterns by turning dots on and off by clicking on them. Designed so you can just mess around with it. Record patterns, make new samples and export them as .wav files, record sounds. MIDI aware so you can plug your favorite MIDI device in and use that as the UI. Supports multiple audio drivers, too. There are versions for Apple iOS, Android, Windows, OSX, and Linux. Samples are delineated with Space Invaders-style sprites so you can tell them apart.
Pushover is a pushnotification site that just gives you an API to work with and a near-universal app that runs on Android or iOS. Add realtime notification to whatever you want with nearly no work. The app's free for a week; after that you have to pay $5us for a perpetual license. You also get 7500 notifications per month per integration.
An openstreetmap app for android which keeps tabs on your GPS coordinates and shares your location in an anonymous fashion with a random Target ID and tracking code. Can share with chosen people or the public at large. Can transmit and receive data via SMS.
A personal webapp for tracking your own location. Lets you set up a private location diary or a realtime tracker to share with people you give access to. A phone app for iOS and android is the user front-end. The app can publish GPS coordinates and your phone's status to an arbitrary HTTP API endpoint or MQTT broker if you tell it to. Your location gets plotted on a map. The back-end is called Recorder and is found on github: https://github.com/owntracks/recorder
FOSS AI personal assistant software. Implements actions/useful features, skills and API connectors. Can answer questions and ask for context for better answers (interesting!) Has a dedicated android app as well as a web interface. Written in Java, but nobody's perfect.
voice assistant speechrecognition exocortex Designed for privacy, runs on-device on-prem, works without a network connection. There are community contributed skills, called snips, provided skills, and you can develop your own with a web based visual builder. Supports multiple human languages. Deploy to your own devices as long as they run android or linux. github repos here: https://github.com/snipsco
A crowdsourcing service which lets lets people who are visually impaired call for visual assistance from their smartphones.