You may be familiar with Éric Lévénez and his excellent Unix history timeline, in printable PDF format. Éric also maintains a parallel history of Windows and DOS - which now includes FreeDOS. Check it out: http://levenez.com/windows/
"I was very busy these days, but finally I have updated my windows chart by adding FreeDOS and DR-DOS. I used your chart but also Wikipedia for the dates and releases. I have taken only a simplified version for the FreeDOS and the DR-DOS history, but I think it is more clear like that."
We also have our own timeline chart at http://www.freedos.org/freedos/news/press/2006-doshist.txt