Here is the list of  Top 10 Mostly Downloaded Plugins of WordPress.This list may be very helpful for you if you’re new to WordPress or setting up a new WrodPress Blog.
1) All in One SEO Pack
Automatically optimizes your WordPress blog for Search Engines (Search Engine Optimization).
Website Click Here

2) Google XML Sitemaps
This plugin will generate a special XML sitemap which will help search engines to better index your blog.
Website Click Here

3) Contact Form 7
Just another contact form plugin. Simple but flexible.
Website Click Here

4) WP-PageNavi
Adds a more advanced paging navigation to your WordPress site.
Website Click Here

5) Akismet
Akismet checks your comments against the Akismet web service to see if they look like spam or not.
Website Click Here

6) BuddyPress
Social networking in a box. Build a social network for your company, school, sports team or niche community.
Website Click Here

7) Sociable
Automatically add links on your posts, pages and RSS feed to your favorite social bookmarking sites.
Website Click Here

Google Analytics for WordPress
The Google Analytics for WordPress plugin automatically tracks and segments all outbound links from within posts, comment author links.
Website Click Here

9) WP-SpamFree Anti-Spam
Powerful anti-spam plugin that eliminates blog comment spam. Finally, you can enjoy a spam-free WordPress blog! Includes contact form.
Website Click Here

10) Simple Tags
Simple Tags is THE perfect tool to manage perfectly your WP 2.8 and 2.9 tags (Tags suggestion, Mass Edit Terms (Tags and Category), Auto link tags.
Website Click Here

No doubt, WordPress is mostly used and excellent bloging software.Below is the list of 10 Alternative to WordPress.If you are looking for alternative to WordPress you should try them.

1) Serendipity:
Serendipity is a PHP-powered weblog application which gives the user an easy way to maintain an online diary, weblog or even a complete homepage.
Website www.s9y.org

2) Nucleus CMS:
It offers a system that is easy to install, but still offers maximum flexibility and many features.
Website nucleuscms.org

3) SPHPBlog:
Unlike other blog software, there is almost no setup – just unzip and copy.
This blog uses flat text files. It does not require a database.
The main functionality of the blog is to present other people with the text and opinions that you would like to share. For this reason, the blog entries are shown on the very first page they visit.
Website www.simplephpblog.com

4) Habari:
Habari represents a fresh start to the idea of blogging. The system is fast, easy to use, and easy to modify. New users should have no problem using and enjoying Habari. Advanced users should have no problem tweaking Habari to do exactly what they need it to do.
Website habariproject.org/en

5) Pixelpost:
It is very heavily geared towards photobloggers and comes with a set of features that caters to photobloggers needs.
It can also be used as a designer’s portfolio, thanks to its great image handling platform.
Website www.pixelpost.org

6) LifeType:
LifeType is an open-source blogging platform with support for multiple blogs and users in a single installation.
Writing articles is comfortable with the included state of the art WYSIWYG editor. Adding pictures and sound files (for Podcasting) is just a matter of browse and click.
Website lifetype.net

7) b2evolution:
It includes all the traditional blog features and extends them with evolved tools like file & photo management, advanced skinning, multiple blogs support as well as detailed user permissions.
Website b2evolution.net

8.) Small Axe Weblog:
The Small Axe Weblog makes setting up your own weblog easy. Unlike some of the most popular weblog tools, Small Axe is designed to be simple and easy to read, so a new developer or even an experienced one can immediately begin creating their own custom application upon it.
Website sourceforge.net/projects/smallaxe

9) Host-Press:
Host-Press is a powerfull php script that allow everyone to build an online bloggers community, offering your visitors to create and host a free blog, based on WordPress.
Host-press is a PHP script, that allow you to offer a free WordPress 2.0 Blog to your visitors. Host-Press has been developed starting from WordPress 2.0.
Website webscripts.softpedia.com/script/Blog/Host-Press

10) Vezir:
Vezir is a new view for blogging and it’s going to support a lot of known web technologies. Except blogging, it can use as a cms.
Website code.google.com/p/vezir

1) iNove

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2) Pixel

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3) LightWord

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4) Atahualpa

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5) Fusion

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6) Arclite

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7) Pyrmont V2

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8 ) Arras Theme

Download Click Here

9) Carrington Blog

Download Click Here

10) monochrome

Download Click Here