Firefox and Inkscape have network effects, albeit more limited than Skype. The more people using Firefox, the more sites work with Firefox. Not a big issue now,

Firefox and Inkscape have network effects, albeit more limited than Skype. The more people using Firefox, the more sites work with Firefox. Not a big issue now, but it was. And Firefox must have spread largely through word of mouth (actually anyone done research on how Firefox adoption did predominantly occur?). More people using Inkscape, more acceptable it is to use, and better it works with files one might receive (assuming Inkscape works a bit better with svg than with Illustrator or whatever that it must import), same for Open/LibreOffice (which definitely works better with ODF than OOXML). All software has network effects to some extent; a significant reason why using free/open source software is a matter of good citizenship, not just getting stuff done.