Context based version of Underscore.js (https://github.com/documentcloud/underscore) micro-templating. General difference is to use object context, instead of with(object) { } statement. It solves problems with undefined variable issues and makes easier to handle it:

Underscore

var html = "<div><%= surname %></div>";
_.template(html, { }); // Will throw "ReferenceError: surname is not defined"

so need to handle that like:

var html = "<div><% if(typeof surname != 'undefined') { %><%= surname %><% } %></div>";
_.template(html, { }); // <div></div>

ContextTemplate

var html = "<div><%= this.surname %></div>";
CT(html, { }); <div></div>

Assume that ContextTemplate function is assigned to CT global variable:

var html = "<div>Name: <%= this.name %> <% if(this.surname) { %><br/>Surname: <%= this.surname %><% } %></div>";
CT(html, { name: "Bob", surname: "Jones" }); // <div>Name: Bob<br/>Surname: Jones</div>

Also it's possible to use @ as a shorthand for this.:

var html = "<div>Name: <%= @name %> <% if(@surname) { %><br/>Surname: <%= @surname %><% } %></div>";
CT(html, { name: "Bob" }); // <div>Name: Bob<br/>Surname: Jones</div>

The other difference is lazy caching, instead of manual caching in _.template. Whenever template function is called for html string, "compiled" result will be saved in cache and next time same template called - cached version will be used:

Underscore

var html = "<div><%= name %></div>";
var compiledHTML = _.template(html); // Stores "compiled" template
compiledHTML({ name: "Bob" }); // Use cached template, just apply new variables
compiledHTML({ name: "Sam" }); // Use cached template, just apply new variables

ContextTemplate

var html = "<div><%= @name %></div>";
CT(html, { name: "Bob" });  // Stores "compiled" template
CT(html, { name: "Sam" });  // Use cached template, just apply new variables