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
True, but I think typically the Playstore version isn’t always from the official maintainers and I’d consider it less trustworthy, even if free (unless the devs link to the playstore page on github/gitlab/codeberg/whatever).
the play store version isn’t as trustworthy even if the original devs published it there, since google forced all developers a few years ago to hand over their signing keys. the signature is how you know the app wasn’t modified by anyone, and that actually the developer released the apk
Yes, a lot of developers have done this. Many examples have been posted on this thread (OsmAnd, Conversations, Davx5) - Mindustry is another example. free on f-droid (and Google store too I think), but $10 on Steam.
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
No. It’s not. Please take a look at different licenses in this area, whatever ‘libre’ means
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.
Conversations, an XMPP chat app, does exactly this.
Free software is a matter of liberty, not price. It is perfectly legal and ethical to sell free software. Keep in mind if you’re using third party code (whether it’s libraries or external contributions to your application) you must abide by the terms of whatever license it is under, this is whether it’s paid or gratis.
It’s even perfectly legal to fork an existing free software project and sell it on the play store, although whether that is ethical or not is up for debate - depending on what efforts you put into your fork before selling it, an orthodox Stallmanist might have no problem with it but the original developer(s) of that code may perceive this as “theft.” Keep in mind you must abide by the terms of whatever license the project is under, so if it is a copyleft license like the GNU GPL you must either provide corresponding source code or an offer for such.
