Simple Mobile apps have been very popular among FOSS enthusiasts. I've personally been using the Gallery, Contacts and the Phone app since a few years now. It's a shame that it has come to this, will be on the lookout for their forks.
Because freeloaders who call themselves "open source enthusiasts" aren't really good at supporting people who create them. It's often quite the opposite. Rude, entitled, and ungrateful bunch of whiners that want everything free and some more. Then act surprised after their favorite opensource app is shutdown, sold or archived.
This guy even had paid apps on the playstore so whoever says "but opensouce doesn't mean you can't sell em" can fuck right off.
And you think the solution is to sell to a company that will instantly add data mining and ads? Often to those users, for whom we have installed these apps, but from google play for the automatic updates?
They might've done so out of necessity. I don't know if the dev(s) of the Simple Tools apps were working on it full time, but if they were and just not enough contributions were coming in from it... Well everyone has to eat.
As the saying goes, "everyone has their price". It's easy to condemn the developers for their choice until you're in the exact same scenario as they were. Whether that's because they were starving, or even just offered enough money to make their lives a lot easier - not too many people would turn it down.
That one doesnt have the security vulnerability and I think it is also better. But they are pretty much equal.
Simple Gallery - Aves
I prefer Simple Gallery though, it is pretty great
Simple dialer - Welefon
Very basic, I personally use ACR phone for call recording, with disabled internet permissions. The Dev asked on Reddit about opensourcing the App and got negative responses, so maybe unlikely.
Simple Keyboard - Florisboard
Currently unmaintained but awesome. I hope it gets revived.