V$INSTANCE

Columns
   ___________________________
 
   INSTANCE_NUMBER
   INSTANCE_NAME
   HOST_NAME
   VERSION
   STARTUP_TIME
   STATUS
   PARALLEL
   THREAD#
   ARCHIVER
   LOG_SWITCH_WAIT
   LOGINS
   SHUTDOWN_PENDING
   DATABASE_STATUS
   INSTANCE_ROLE
   ACTIVE_STATE

Related:

V$ACTIVE_INSTANCES 
V$BGPROCESS 
V$BH 
V$COMPATIBILITY 
V$COMPATSEG 
V$COPY_CORRUPTION 
V$DATABASE 
V$DATAFILE 
V$DATAFILE_COPY 
V$DATAFILE_HEADER 
V$DBFILE 
V$DBLINK 
V$DB_PIPES 
V$LICENSE 
V$OFFLINE_RANGE 
V$OPTION 
V$SGA 
V$SGASTAT 
V$TABLESPACE 
V$VERSION