Unlike NING, Elgg provides the code for you to setup your own social network.

Requirements
Elgg 1.0 requires a system running PHP 5.2+ as an Apache mod (not in CGI mode or safe mode) with GD extensions, MySQL 5+ and a version of the Apache web server with mod_rewrite installed. OpenSocial requires Mcrypt; Elgg 1.1 SOAP extensions will require the PHP SOAP library.

End-user features
Profile
Dashboard
Activity feed
User preferences
Comprehensive administration tools
OpenSocial applications
Blogging
File repository
Forums
Social bookmarking
And more..

Check out http://www.elgg.org

ReVou is a PHP micro-blogging social networking software that allows you to start your own site just twitter and Jaiku at an affordable price!

Features

100% source codes
Affordable (Pay Once)
Online Download
Multi-Language
Template Driven
Free 1 year updates
Support from ReVou
Built-in API
SMS Integration
Supports SMS/IM/Web
Twitter Plugin
Google Maps Integration
Widgets Plugin
Self-hosted platform
And many more!

Check out http://www.revou.com/index.php

Smashing Magazine’s study of blog design provides a good insight of the design trends/patterns are mostly used by top blogs on the internet.

Excerpt from the article

large blogs require a multi-column layout solution (usually 3 columns suffice) (58%);
layouts are usually centered (94%),
layouts usually have a fixed weight (px-based) (92%),
the width of the fixed layout varies between 951 and 1000px (56%),
58% of the overall site layout is used to display the main content,
CSS-layouts are used (90%),
the background is light, the body text is dark (98%),
the most usual (not necessarily most user-friendly) line length lies between 80 and 100 characters,
Verdana, Lucida Grande, Arial and Georgia are used for body text (90%),
the font size of body text varies between 12 and 14px (78%),
Arial and Georgia are used for headlines (52%),
headlines have the font size between 17 and 25px.

Read more

LimeSurvey - The open source survey application

LimeSurvey basically contains everything you need for doing nearly every survey with grace.

Having said that Lime Survey offers innumerable features required for setting up your own survey in your own way. A few features would be…

# Unlimited number of surveys at the same time
# Unlimited number of questions in a survey (only limited by your database)
# Unlimited number of participants to a survey
# Multi-Lingual Surveys
# User-Management
# 20 different question types with more to come
# WYSIWYG HTML Editor
# Quotas Management
# Integration of pictures and movies into a survey

This is just a fraction of features offered by LimeSurvey…So check out the LimeSurvey site and get refreshed!

Features

I have been exploring some photo blog applications on the web and finally thought of giving a try to PixelPost. Seems a good option for people who want to build a photo blog.

Pixelpost is an open-source, standards-compliant, multi-lingual, fully extensible photoblog application for the web. Anyone who has web-space that meets the requirements can download and use Pixelpost for free!

Features:

Smooth Install Assistant
New Template Tags
Cool Feed Options
Brand New Front Workspaces
more…

Official website