Article directories are used by webmasters for search engine optimization. Some popular articles directories are really used by people for reading or learning about any topic they wish. People post their unique articles in such articles directories for getting valuable back links (normally 3 back links are allowed per article) and for getting visitors to their websites. Webmasters use the article directories to find out good articles for their sites.
Some articles directories popular with the readers are EzineArticles.com and GoArticles.com
There are indeed many like articlesbase.com, articledashboard.com, etc.
There are also some domain specific articles directories like travel articles directory, health related articles directory, games / gaming, law / legal, sports related, educational articles, etc.
There are many free and paid article directory scripts available. Here i am listing some articles directory scripts. These have approve option in the admin interface. Most of the script sellers will send you screenshots of the admin interfaces / management control panels of the software if you email them using the help or contact link on their websites.
Article Dashboard: It is the most popular script but is known to suffer from hacking attempts. Its an open source script. You can get it free from the Article Dashboard website.
The next in popularity rankings is the Article MS Script. Learn about it at ArticleMS.com
There are many more article directory scripts. More keep getting launched:
Article Friendly script. See articlefriendly.com
Munius is a article directory software for webmaster who want to set up their article directory. It allows comments by members.
www.munius.com
There are some directory scripts which claim to have thousands of articles in its database. I am not really sure if they really work or not. But i have heard webmasters complaining after purchasing the articles scripts alongwith the databases. There are many security related issues with such databases.
An article directory which has a huge database of articles with it is
www.yourarticlesdirectory.com
E-Soft24
It is an seo friendly articles directory software for webmasters. Visit the website
www.e-soft24.com
www.ozwebfx.com/articledirectory
Another script
PHParticlescript.com
Its heavily promoted by PPC on search engines. Must check this one.
You may buy an open source php, cgi or perl script with good control panel / management console and go for modification or customization in the support forums or on top freelancer sites. Good luck!