Do you think jQuery API serve the purpose of being most popular client side API in today's world?

In the today's web applications, JQuery is serving in a quite better way to handle the client side API. Different developers have different type of experiences with JQuery according to the requirement of the web applications. As mentioned below by some developers, it is mainly used for DOM modification. Its features become limited when developing a highly advanced web application. you will have to take resort of other javascript frameworks like ExtJS, Dojo to develop such applications. But overall JQuery is serving better in the mid type client side API.

jQuery is mostly for DOM manipulation, i doubt it will ever have those features mentioned, that's why they mix it with libraries like Backbone, i really don't like jQuery, sadly i have to work with it with other developers who write very bad JavaScript code, i use Dojotoolkit most of the time, its a very good framework.

Right Remi, that's the point I want to bring up there, we know jQuery is user friendly but when it comes to complex part it's rather uselss, you could only do Dom manipulation and AJAX other then it doesn't have much to serve.
You can find the below point wrt jQuery -Fast -Well documented -Easy to use -Chaining -Unlike Prototype it doesn't extend an object if you didn't specifically ask for it (try looping an array in Prototype) -easy-to-use Ajax (I love the $.ajaxSetup() function) -Nice event handlers -CSS selectors -filtering your selection -Small size -Nice little built-in effects -Plugins I have been using Dojo with DojoX probably the most underrated JavaScript framework bit hard to adopt specially if you are a jQuery lover, it's not straight forward and I kinda like Dojo a lot.
-OOP (and other paradigms) done right -Widget infrastructure done right -Modules done right with all necessary goodies: -Lazy loading of modules dynamically -Possibility to extract only necessary modules and build a custom one-file profile -Asynchronous loading of modules if desired -Simple integration with CDNs for heavy-duty web applications -Sheer breadth of available modules in DojoX including graphics, charting, grids, and so on -Ability to use it in non-browser environments -Attention to details in widgets: -support for i18n (including LTR and RTL languages) -support for l10n (including standard date, currency, number formatting) -provisions for people with special needs (automatic high-contrast mode, keyboard-only support, and so on) — useful for regular users too, and mandatory for most government contracts The problem is, most of the seasoned developer's always want to use jQuery without thinking other available frameworks, for large enterprise apps one should always consider MVC (using ExtJS, Dojo MVC, JavaScriptMVC, backbone.js etc.) One always have choice, don't try to restrict your imaginations.

You can find some web application base is Jquery.
I personally use Jquery alot, and it's becoming very popular, and it has a very good documentation.
But You can find others like YUI, mostly yahoo developers use it.
Kendo Web, but it uses some of JQuery functions and bases.
and As Okeowo wrote, it's amazing and great for DOM manipulation.