.org is the domain for non-profit organisations and open source projects. It is a domain that stands for reliability,
for idealism, engagement and democracy. An .org extension communicates the message that a website is not made mostly
for the benefits of the webhost, but for the user.
So if you want to make a website that you want to come across as reliable and engaged, then .org is a good choice.
History:
.org was one of the six original extensions that were launched together in 1985.
Apart from .org those were .com, .edu, .mil, .net, .com and .arpa. The idea was that each extension would serve a
different target: .edu was meant for educational purposes and .gov for websites of governments.
.org was the domain extensions for all the websites that did not fit in all the other categories.
In actual practice it became the domain for non-profit organisations and other not-commercial enterprises.
Despite this conscious choice for a target, registering a .org domain has never been restricted.
Everyone who wants to register a .org domain, can do so. Because of this, there are also some commercial corporations that
have a .org domain. This kind of use of the extension may be controversial, but it is not actively opposed to by the register.
For a while, .org was also promoted as a domain for private websites and for informative websites,
but for those purposes .name and .info were later introduced.
Current use:
Because of its non-commercial image, .org is popular with charity organisations and website that are related to the
open source movement, where visitors and users can contribute themselves to the product or website that they're using.
Examples of this are the website of the open source office software package http://www.openoffice.org and the online
encyclopedia http://www.wikipedia.org.
In 2009 it was announced that .org is the first generic top-level-domain that will start using DNSSEC,
an initiative to fix the vulnerability for hackers of the normal DNS-zone.
This only underlines the safe image of .org and makes it even more interesting.
Another good argument to start considering ordering your own .org domain.