Secure office and productivity apps
Gnumeric
Gnumeric is an open-source spreadsheet program.
Calligra
Calligra Suite is an office and graphic art suite by KDE. It is available for desktop PCs, tablet computers, and smartphones. It contains applications for word processing, spreadsheets, presentation, vector graphics, and editing databases.
Free Office
LibreOffice is a powerful and free office suite, used by millions of people around the world.