I don't know about you, but I am getting increasingly bothered about the vast numbers of dubious permissions, unwanted tracking ads, and risky bits of software available via Google's App Store. F-Droid is a fully open source replacement for the AppStore (though it can be used in addition to the App Store) that only carries open source apps, the vast majority of which have been built from source and verified by the F-Droid community. The app itself is friendly and easy to use. The F-Droid website is great and, as a bonus, includes a great list of apps with anti-features - https://f-droid.org/wiki/page/AntiFeatures - that you probably don't want to have installed on your phone or tablet.

The main downside is that the selection of apps available is understandably small, but there's enough stuff here to cover most things you'd be likely to need on your phone (not including closed social sites like Facebook, Twitter, etc, shopping sites, etc, etc). There are also a few limitations here and there, such as inability to automatically update all apps when new versions come around, most of which can be overcome if you have a rooted phone and/or are very brave and committed to getting rid of everything else on your phone but open source tools. I'm not that brave/foolhardy/time-rich, but any proprietary and risky apps that I can replace with free, open and safe apps seems like a bonus to me.

I still have some fairly major concerns about the preinstalled apps and firmware on my phone that are much harder to get rid of, but this is a great step forward.