List TABLEs, SEQUENCEs or INDEXes in Oracle:

-- list TABLEs
SELECT object_name FROM user_objects WHERE object_type = 'TABLE';

-- list SEQUENCEs
SELECT object_name FROM user_objects WHERE object_type = 'SEQUENCE';

-- list INDEXes
SELECT object_name FROM user_objects WHERE object_type = 'INDEX';