Easy to set up versioned and synchronised directory/file system

Users (or administrators) should be able to easily set up versioned directories (or /home file systems). If set up, (a) old versions of overwritten files in that directory should be recoverable, and (b) the entire directory should be easily synchronised (e.g. between desktop and laptop). It should be configurable that after a merge only one of the hosts (desktop or laptop) keeps the history, the other only the latest version (and all changes since the latest merge).

In normal usage, having versioning should be completely transparent, both in the GUI as in the command line. Commit should be automatic, not a manual command. In versioned directories/file systems, application should not keep tilde~ backups of the next-to-latest version or use other similar workarounds. In a sense, Trash is also a workaround of not having versioning. For versioned directories, Trash contains "links" to the latest version (in the versioning system) of trashed files.