1. A computer implemented method for dynamically enabling customized web content and applications, comprising: storing, by a custom content server, one or more rules in a database, each rule comprising a condition and an action; transmitting, by the custom content server, default tag code to a browser executing on a computing device in response to a request from the browser, the default tag code including data that causes the browser to generate a tag module in a memory of the computing device; receiving, by the custom content server, an update from the tag module comprising data indicative of a visitor's interaction with web page content displayed through the browser; determining, by the custom content server, a condition associated with a rule from the one or more rules is satisfied based on the update; and performing, by the custom content server, an action associated with the rule, comprising transmitting custom targeted tag code to the tag module, wherein the custom targeted tag code includes data that causes the browser, upon execution of the custom targeted tag code by the tag module, to perform an action.