Hi Koen,

this sounds like what you actually need is a version control system like SourceSafe, Subversion, SourceVault, CVS, etc. Most systems are free for one or two developers. Subversion is open source and therefore free for all developers. There are several articles on using Subversion with VFP:

http://www.foxpert.com/docs/cvs.en.htm
http://www.west-wind.com/presentations/subversion/

plus some tools

TwoFox: http://www.foxpert.com/download/twofox.zip
SubFox: http://vfpx.codeplex.com/Wiki/View.aspx?title=SubFox
ScX: http://paulmcnett.com/scX.php