All below are free to develop, deploy and distribute. But first of all joining to Oracle Technology Network(OTN) community is free http://www.oracle.com/technology/membership/index.html and you will be needing a membership for below mentioned resources.

A. Download and Install Oracle Enterprise Linux

        download - http://edelivery.oracle.com/linux

        installation guides - http://www.dizwell.com/prod/node/694 and http://www.puschitz.com/ and http://www.oracle-base.com/articles/linux/ArticlesLinux.php

        OTN forum support - http://forums.oracle.com/forums/forum.jspa?forumID=135

        official support if needed(extra cost) http://linux.oracle.com

        OTN portal - http://otn.oracle.com/linux

        From my blog - Oracle, Linux and Shell Scripting Part 1 - http://tonguc.wordpress.com/2007/01/14/oracle-linux-and-shell-scripting-part-1/

B. Download and Install Oracle Express Edition(XE) 10g Release 2

        download - http://www.oracle.com/technology/software/products/database/xe/htdocs/102xelinsoft.html

        installation guides - http://download.oracle.com/docs/cd/B25329_01/doc/install.102/b25144/toc.htm

        OTN forum needs extra registration(free) - http://www.oracle.com/technology/xe/registration

        OTN forum support - http://forums.oracle.com/forums/forum.jspa?forumID=251

        official support N/A

        licience guide for limitations - http://download-uk.oracle.com/docs/cd/B25329_01/doc/license.102/b25456/toc.htm#BABJIJCJ

        all documentation - http://www.oracle.com/pls/xe102/homepage?remark=tahiti

        OTN portal - http://otn.oracle.com/xe

        From my blog - Oracle Express Edition(XE) and Application Express Part 1 - http://tonguc.wordpress.com/2007/01/15/oracle-express-editionxe-and-application-express-part-1/

        From my blog - Oracle Express Edition(XE) and Application Express Part 2 http://tonguc.wordpress.com/2007/08/28/oracle-express-editionxe-and-application-expressapex-part-2/

C. Upgrade Oracle Application Express(ApEx-formerly HtmlDB) to version 3.0

        download No need, comes within XEbut if needed http://www.oracle.com/technology/products/database/application_express/download.html

        installation guides - No need, comes within XEif needed http://download.oracle.com/docs/cd/B32472_01/doc/install.300/b32468/install.htm#CHDHIJGE

        upgrade guide - http://www.oracle.com/technology/products/database/application_express/html/3.0.1_and_xe.html and http://forums.oracle.com/forums/thread.jspa?messageID=1961436

        OTN forum support - http://forums.oracle.com/forums/forum.jspa?forumID=137

        official support if needed(extra cost) http://metalink.oracle.com

        online development center - http://apex.oracle.com

        ApexLib Framework - http://inside-apex.blogspot.com/2006/12/quick-overview.html and http://apexlib.sourceforge.net/

        OTN portal - http://otn.oracle.com/apex

        From my blog - Oracle Express Edition(XE) and Application Express Part 1 - http://tonguc.wordpress.com/2007/01/15/oracle-express-editionxe-and-application-express-part-1/

        From my blog - Oracle Express Edition(XE) and Application Express Part 2 http://tonguc.wordpress.com/2007/08/28/oracle-express-editionxe-and-application-expressapex-part-2/

D. Download and Use Oracle SQL Developer Development Environment

        download http://www.oracle.com/technology/software/products/sql/index.html

        installation guides http://download.oracle.com/docs/cd/E10405_01/doc/install.120/e10407/toc.htm

        OTN forum support - http://forums.oracle.com/forums/forum.jspa?forumID=260

        official support if needed(extra cost) http://metalink.oracle.com

        information exchange center - http://sqldeveloper.oracle.com

        OTN portal http://www.oracle.com/technology/products/database/sql_developer/index.html

And also all software downloads are free with Oracle and each comes with a Development License that allows you to use full versions of the products only while developing and prototyping your applications (or for strictly self-educational purposes). You can buy products with full-use licenses at any time from the online Store or from your sales representative.