This great Oracle instance discovery tool. The tool does not need an Oracle client and is not a wrapper on top of the Oracle client. It can be used to interrogate the Oracle listener to display information about remote (and local) listeners - For instance services, SID, listener statistics on established connections. The link above points to Paul's main page for this tool and it gives some details of the tool and also some graphics of it in use. A great feature is the fact that a working TNSNAMES.ORA connection string is stored in the Windows clipboard. As I said the tool does not use Oracle libraries / OCI etc. It used native network code to send packets to the listener. The free version does not support all listener commands, the Pro version does. The free version does not support TNSPings, Paul was going to release a free ping tool, but this never happened.
I have updated my Oracle Security Tools page to update the new link.