If 'multi-user' is a 'feature' then I think we have a clear winner. There are packages to patch on to Access which allow 'multi-user' though I don't know if/how well they scale.

Also direct network access might be construed as a feature if ODBC isn't desired as the interface.

Also, some may consider portability a feature.

Authentication and access control are also widely considered to exist in the 'feature' space.

I am sure there are others in addition to this very brief list.