The Open Source is an exciting world.
plugsys. Let's define 'Open Source': it is software distributed with the source code that anybody can study, modify for their own needs and redistribute. It is often also free (it costs nothing).
If you want to know more, go to http://www.opensource.org/, and http://en.wikipedia.org/wiki/Open_source.
Harbour, xHarbour and Clip are released under the GNU General Public License (GPL) plus an option that allow the users to distribute the applications they develop under the license they wish (if they were to follow strictly the GPL they would have had to distribute their applications under the GPL). The GPL is the license adopted by the GNU project, and it makes it perhaps the most famous Open Source license because an entire operating system is released under it - the OS that is commonly referred to by the name of its kernel, Linux.
Links for "what is the GNU Project?", "what is the General Public License?", "what is Linux?".
For more informations visit http://www.gnu.org/gnu/thegnuproject.html and http://en.wikipedia.org/wiki/GNU, http://www.fsf.org/licensing/licenses/gpl.html, http://www.linux.org/.
In addition to the GPL, Clip offers optionally a commercial license. The user can choose which license applies to his installation.
x2c is released under the Apache license. The most important software released under the Apache license is Apache, a widely used open source web server.
http://en.wikipedia.org/wiki/Apache_HTTP_server and http://en.wikipedia.org/wiki/Apache_License.
Now a word about the GNU Free Documentation License (FDL) license.
Now you should be convinced that open source is good. Now see that xBase is good, too.