Explain what is the difference between Borland Silk and Selenium?

Silk Test Tool:

 Borland Silk test is not a free testing tool
Silk test supports only Internet Explorer and Firefox
Silk test uses test scripting language
 Silk test can be used for client server applications

 Selenium Test Tool:

 Selenium is completely free test automation tool
Selenium supports many browsers like Internet Explorer, Firefox, Safari, Opera and so on
 Selenium suite has the flexibility to use many languages like Java, Ruby,Perl and so on
Selenium can be used for only web application