[Cialug] Slightly OT, .. File sharing with locking?

[L. V. Lammert]

Trying to figure out we could share an app between two users for my Mom's
family. Dropbox will allow us to share the files, *BUT* there is no way to
know if someone is in the process of changing the file.

Has anyone ever seen such a public service (svn or git would perfect, but
I'm the only that could spell vesion control) that would provide an option
to lock the file?

	Lee