The same opensource app, downloadable on both stores but paid on playstore and free on fdroid. Is it legal and is it ethical? Why?
Sure , indeed there are some foss app that are the same as you described
If you own the copyright then yes this is 100% legal.
There are already apps that are like this. They usually add a couple features to the paid release so that people feel like they are getting something extra for the money. The good ones will eventually move those features to the open release eventually. However, this incentivizes keeping part of the app closed source so that nobody can just rename and re-release the paid version.
It is 100% up to you for how to handle these tradeoffs. Personally, I think so long as you are principled and ready for some criticism - and can handle it gracefully - getting paid for work that builds your open source app is a very good idea. We don't all have the luxury of maintaining high quality unpaid side projects!
If you don't own the copyright and its libre software, this is 100% legal too
An alternative is to have both be the same and have one just be for people who want to contribute monetarily to your efforts or have the convenience of using their preferred store (if playstore is their preferred store). I think that's sort of what Mindustry does (a foss game). It is available for 10€ on Steam, but also available for free on itch, with the steam version just having the benefit of being a steam game and having steam achievements. I guess ethically all is fine if you make clear that the game is also available for free from another place.
It's perfectly legal but personally, I would not find this really ethical: a lot of people don't know F-Droid and if they find your application directly in the Play Store, they won't know they can have it, the exact same application, for free but elsewhere.
I prefere one of those solutions:
- The ability to send a donation, it's a very common thing.
- Having the same application twice on the Play Store, one for free and one with a fixed price (I don't remember which app do this but I saw it once).
Of course this is my point of view, everyone has its own vision of what is ethical or not. Do not take my comment as the absolute truth!
I thought because some people wouldn't know about the app and may think they have to pay
Label the Play Store version as "Pro" but don't actually change anything. It'll have a placebo-like effect and make people feel better about spending money.
