Grant all the privileges to a user over all other user's objects in Oracle
Which privileges?  Of course they are granted by using the appropriate GRANT command, but I suspect that is not what you are asking.  You could use the ANY option (like GRANT SELECT ANY TABLE ...) but I strongly recommend against it as it violates the principle of granting least privilege necessary.  I suspect what you really need is something like this:

set echo off feedback off header off pagesize 0
spool doit.sql
select 'grant select on table '||table_name||' to someuser;'
from dba_tables
where &lt;whatever condition to filter the list of tables&gt;
;
spool off


Then do a sanity check on the spooled file 'doit.sql', edit as necessary, then execute it.  Some do it all in one pop with a PL/SQL loop, but I'd rather capture the commands first and be able to do the sanity check on it.