IBM Lotus
I use it and prefer it to Open Office; it seems a little less clunky.
The important point to note, however, is that the native file formats for IBM Lotus are ODS and all the rest: the same as Open Office. I can edit a presentation in either package, or a WP document, or a spreadsheet.
So, though the program code isn't open source, the file formats are: you can always escape from the embrace of IBM if so inclined.
The one failure in the design of IBM Lotus was leaving out the ability to import .wk4 files. Lotus handles the .123 files introduced some time after R5 of the original Lotus 1-2-3, but that leaves a huge body of spreadsheets still unreadable.


