JRE:

$ORACLE_HOME/jdk/bin/java -fullversion

Version of perl
perl -v

Version of opatch
$ORACLE_HOME/OPatch/opatch version

JDK:
Open your Context File and look for variable
JDK_TOP oa_var="s_jdktop"

How to find Apps Version (11i/R12/12i).
select release_name from apps.fnd_product_groups;

Web Server/Apache or Application Server:
$IAS_ORACLE_HOME/Apache/Apache/bin/httpd -version

Forms & Report version (aka developer 6i) in 11i:
$ORACLE_HOME/bin/f60run | grep Version | grep Forms

Oracle Jinitiator in 11i/R12/12i:
grep jinit_ver_comma $CONTEXT_FILE

Discoverer Version for 11i
$ORACLE_HOME/bin/disc4ws | grep -i Version

Application Server:
cat $ORACLE_HOME/config/ias.properties | grep Version

Oracle Portal
SQL> select version from portal.wwc_version$;

To find database version
SQL> select * from v$version;