for office system, I recommend kingsoft WPS office, which is based on Qt, much faster than java based solution. It has Android, Linux version in alpha, in addition to mature windows ‘s version
For 2D CAD drawing, I recommend Dassault system’ Draftsight, it is a professional level product. just need a email activation. Linux version is still in beta.
Both are not open source, but free of charge for production usage.