Well I don't know a programm for working at the same time on a project but I always use a dropbox for sharing my scenarios with my friends. here is the link to the webside.

You could also use Wuala, which is more secure than dropbox. The only bad thing is that you have less storage, but greenfoot scenario's aren't really big :)

Yes the security dropbox is using is realy not the best so you should not upload sensitive data but I think for greenfoot scenarios it's ok. If you want to upload sensitive data you shouldn't use it.

Thanks for your help. I do already have a Dropbox-Account, but didn't think about using it for this. It is an acceptable Solution for now, so thank you :) Right now my data is not as sensitive, so I will stick to Dropbox, because I have an account there already. But thanks for the information, maybe I'll have to switch to Wuala at a time :) I still would be interested in way to work online at the same time. So if anybody has further Information, it is still welcome, although Gevater and SPower helped me considerately, already. Thank you :)