OpenDocument Reader - OpenOffice Document Reader is an Android OpenOffice and LibreOffice Document Reader!
LibreOffice Viewer - The Document Foundation provides a LibreOffice Viewer for Android.
Sumatra PDF - Sumatra PDF is a slim PDF/DjVu/EPUB/XPS/CHM/CBR/CBZ/MOBI viewer for Windows.
Evince - Evince is a document viewer for multiple document formats: PDF, Postscript, djvu, tiff, dvi, XPS...
Foxit Reader - Foxit Reader is a free and light-weight multi-platform PDF document viewer.
Trello - Infinitely flexible. Incredibly easy to use. Great mobile apps. It's free. Trello keeps track of everything, from the big picture to the minute details.