I'm not sure of the details, but what used to always be
o Completely free
o Completely ad free
o Simple powerful tools
Has started to not be free (I think) on Google Play as of (I think)
November 2018.
I think they're still free on both GitHub and on F-Droid.
I'm not sure of the gory details, but I was downloading the
SimpleMobileTools apps (which are pretty much some of
the best single-purpose apps on F-Droid) when I noticed
that they're not all free anymore (at least on Google Play).
I "think" the free apps still exist (temporarily?) alongside the
newly-payware apps, so, if that's the case, I'd suggest you pick up the
free APKs now (while you can).