Haven't heard of sailfish. What's the app market place like and who makes the OS?
There are several.
It starts with the integrated Jolla marketplace (Harbour, which, sadly, doesn't offer a web interface to browse apps).
This marketplace has the most "stable" apps, as they're generally maintained by either the Sailfish core team or some "trusted" developers, but it's a pretty empty marketplace.
If you can't find what you want, then OpenRepos is your way to go, it's basically AUR for Sailfish, and offers a great range of native apps for many purposes.
To interact with OpenRepos right from the phone (because going on Internet is annoying), the fairly good Storeman app is fit.
If you want to install and manage some android apps, surely, F-droid is the way to go, as it provides the cleanest and lightest apps, but as every FOSS project, it's not "filled" with every kind of app, so if you really need to find some specific apps, there are a few apps and services (I never tried) that provide a "front-end" over Google Play, allowing you to download and manage GPlay apps without a google account.
Now, for a bit of story, as this page explains in a more detailed version, SailfishOS is a project started by the core team of the MeeGo OS, which was a joint effort between Nokia and Intel for a linux-based operating system.
The biggest advantage I think I can find on my sailfish x phone is the ability to run ARMv7-built Linux softwares and daemons.
Want GPG for your e-mails? Well, install gpgv2.
Want syncthing without a huge service running in the background? Install the linux syncthing daemon and you're set.
Want to use your phone as a pi-hole for 4g tethering? Well, sure, why not.
That seems crazy awesome for someone looking for a really personal experience with their phone or who wants to play with IOT and a smartphone.
Though I worry that it has the classical Linux problem of having too much freedom/ requiring too much technical know-how for your average user to really jive with.
Well, the base project is a professional-oriented OS, sooo
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