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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.
Github repository: https://github.com/cryfs/cryfs
Linux gui frontend: http://mhogomchungu.github.io/cryfs-gui/
Project currently works only in OSX and Linux.