securefs[1] is a command line tool and it works on Linux, Windows and MACOS. This tool does folder based encryption.

SiriKali[2] is a Qt/C++ based GUI tool that acts as a front end to securefs and it works on Linux, Windows and MACOS.

These two tools make secure management of files between the three operating systems and cloud storages very easy.

[1] https://github.com/netheril96/securefs

[2] https://mhogomchungu.github.io/sirikali/