<p>I have access to an Oracle server that has some databases that I would like to access. However, the machine that I have access from has none of the oracle client software. Is there any alternative to oracle's client software the provides the functionality of something like MySQL's mysql or Postgres' psql? I'd like to be able to poke around a bit in the database before writing software against it.</p>

If you download the
free
Oracle Instant Client
you'd be able to use any JDBC or ODBC Database tool such as
DbVisualizer
or
SquirrelSQL
.  Those are GUI tools; I've not come across a JDBC command line tool but there may be one out there.
Alternatively, there is an
Instant Client version of SQL*Plus
which will give you an Oracle
```
sqlplus
```
command line without a full Oracle install.