Hi Axel, for surfaces the script Pilou shows above will show the "naked edges" of the object, those are edges that only belong to one surface and are not joined between 2 surfaces like a solid needs to have.

For working on curves only and not solids, there is a script here that will mark the end point of open curves with a point object so you can see where to investigate for gaps or cross-overs:
http://moi3d.com/forum/messages.php?webtag=MOI&msg=2888.11

- Michael