The FireMonkey framework (commonly abbreviated to FMX) allows cross platform development for Windows, MacOS, iOS and Android from the same code base (either Delphi or C++).
A very common question is “when is FireMonkey for Linux coming?”. Embarcadero are regularly asked this and their reply is always along the lines of “we are keeping an eye on it but at present the market place doesn’t make it worth while”.
Developing general purpose tools for Linux is challenging because there are so many different versions of Linux out there.
However one firm ARE promoting FireMonkey for Linux – using Delphi as the supported language.
Interested parties may like to take a look at FMX for Linux