The best way to install them is through the F-Droid store, which is a catalogue of FOSS software for Android. It’s installable by downloading the .apk file linked on the front page of the F-Droid projec’ts website. The mentioned apps from the Karlsruhe Institute of Technology can then be found by searching for “SECUSO”, which is the name of the research project behind them all.
Alternatively, you can also get them through the Google Play Store under this link or again by searching for “SECUSO”.
In particular, I recommend getting the QR code reader, because many of the free-to-use scanners route everything you scan through their servers, so they’re obviously collecting your data.
Yeah, I have an older Motorola phone that I’ve used to try and get Android alternatives, and none of those three systems will work on my phone. It doesn’t look like any of them will work on my new phone either, but that might just mean I have to try it.
Google/Android also seems to make it as difficult as possible to install any alternative system. The easiest I saw was /e/OS because it was all automated, but after about 10 minutes it informed me that my Motorola phone just wasn’t supported.
There’s such a long ways to go with this sort of thing, but I think it’s pretty clear that the world desperately needs a user-friendly, non-corporate alternative to Android/iOS.
It’s really a bummer that we’re all carrying around powerful little computers with us but the corporate operating systems for them use much of that processing power for their own data collection/profits/purposes and tries to prevent us, those of us who own the phones, from using that power for our own purposes.