The qsessions script will display the user details for any sessions except sys conneted the database and a sum count of the user connections by schemaname.
col machine format a30
col username format a15
set lines 1000
set pages 128
select sid, serial#, username, status, schemaname, machine, service_name from v$session where username !=’SYS’;
select schemaname, count(*) as connections from v$session
group by schemaname;