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
http://wps-community.org/download.html
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.
http://www.3ds.com/products-services/draftsight-cad-software/free-download/
Both are not open source, but free of charge for production usage.