[robkblue]

Do I understand it correctly that for an open source email app like K9 mail as an example, I could download the source code in and alter it in Android studio, do my own programming and use it for my own purposes etc?

[B. Diddy]

I moved this from the Nougat forum to the Developers Lounge, since I think it might be a better place for this kind of question.

[Rukbat]

Sure - if you know programming, if you know Java and if you know the Android environment.

If you're just the usual user, about the best you can do is make it not work, or make it non-compilable, but if you know what you're doing, the only limitation is that you can't modify it to look different and then present it as your own. That's the whole idea of open source - modify it to do it your way.

[pbksoft]

Just note that every software (including open source) has its license. This license tells you what exactly you can do with the source code. For example there might be restrictions on using the modified software for commercial use or enforcement to publish derivative work as open source as well. So generally instead of relying on answers from places like this forum, I would rather suggest reading the whole license...