Over the last ten years, SNSs have evolved from general friendship sites (e.g. SixDegrees.com, Friendster, Classmates, MySpace, Facebook) to more specific hobby-related and career-focused sites.

There are online communities for virtually everything imaginable, and these sites can be broadly categorized into four possible areas:

• Dating/friendship
• Alumni networks
• Career/business related
• Hobby/group networks

These four basic categories can be further organized into the following areas:

Book Communities
Book-related SNSs join together booklovers who want to share their interests in books and authors. Some of these communities allow members to exchange their books with one another. SNSs include: BookCrossing.com; BookMooch.com; BookSwim.com; Revish.com; and Shelfari.com. This category could have fit within the Hobby category below, but there are too many sites in this category to get lumped into hobbies.

Business Networking & Professionals
Business networking communities are places for like-minded professionals to gather and connect with others. The fastest growing community for business professionals is LinkedIn.com. Other SNSs in this category include: CompanyLoop.com; FastPitch.com; Mediabistro.com; and Xing.com.

Family
The family-based SNSs are a places for families to stay connected to each other. These communities can be private so that only family members may access the sites. SNSs in the family category include: CafeMom.com; Family 2.0; Famster.com; Geni.com; Kincafe.com; myfamily.com; and The Family Post.

Friends
The main reason why people join SNSs is to stay connected to “friends.” So the majority of these online communities are built to support these “friendships.” Sites in this category include: 43 Things; Badoo.com; Bebo.com; Facebook.com; Friendster.com; hi5.com; Multiply.com; MySpace.com; Orkut.com; Pownce.com; Vox.com; and Xanga.com.

Hobbies & Interests
There are many online communities built around hobbies and interests. These types of SNSs include sites for people interested in arts, politics, movies, environment, cats, etc. Sites in this category include: BottleTalk.com; CircleUp.com; Coastr.com; Flixter.com; Greenvoice.com; MyCatSpace.com; MyDogSpace.com; vSocial.com.

Languages
Language communities are developed to help people learn a foreign language online. Members network with each other to find a partner to practice language skills. Sites include: Chaula; FriendsAbroad.com; iTalki.com; and KanTalk.com.

Video Sharing
Online video sharing is one of the most popular trends in SNSs. Members in these communities upload video, develop their own videos, share videos, and comment and/or rate videos. SNSs in this category include: BlogTV.com; Buzdeo.com; GodTube.com; MetaCafe.com; Stickam.com; and YouTube.com.

Photo Sharing
Photo sharing communities allows members to upload their own pictures, rate and comment on other people’s pictures, and share pictures with others. Some of these sites incorporate photo editing features and provide people with private libraries that they may share with only people they invite. Sites in this category include: Clickfriends.com; Flickr.com; Fotki.com; Snappages.com; Picasa.com; and Zoomr.com

Audio Sharing
Music sharing communities are among the most popular niche SNSs. Depending on the community, members can develop their own music jukebox, and share their play lists with anyone. This allows people to discover music from friends, and find recommended artists and albums based on their particular music interests. Sites include: Last.FM; Pandora.com; iLike.com; Imeem.com; and Radioblog.com.

Mobile Communities
One of the latest movements in social network communities is mobile phone based networks. Sites include: CrackBerry.com; Jaiku.com; Mozes.com; Socialight.com; and Wattpad.com.

Shopping
Shopping-themed SNSs allow members to share sales, discounts, comments on recent purchases, and research what others have said about products. Sites include: AgentB.com; MyStore.com; Productwiki.com; RedFlagDeals.com; and en.shoppero.com.

Social BookMarking
Social Bookmarking websites are for members to store their favorite links on the web. Links can often be tagged and viewed by anyone. The most popular linked websites can often be added to the most popluar links pages on these sites. Social bookmarking sites include: i89.us; BibSonomy.com; BuddyMarks.com; Clipmarks.com; del.icio.us; Digg.com; Ma.gnolia.com; Netscape.com; Reddit.com; Simpy.com; and StumbleUpon.com.

Students
SNSs in this category are primarily for students. This category used to incorporate Facebook.com, but that site has opened up to include everyone. Sites include: AlumWire.com; Campusbug.com; College.com; RateMyProfessor.com; and StudentSN.com.

Travel & Locals
The travel-themed SNSs are a way for members to connect and learn about destinations they want to travel to or have already traveled to. It’s also a way for people to meet locally. Sites include: Citizenbay.com; Going.com; Outside.in; TravBuddy.com; Tribe.net; and Zoodango.com.

The categories listed above are very broad, and can’t encompass the intricate details of each of the social networks found within them. This condensed categorization is merely a general overview of how these various communities might be grouped. Many of these SNSs could easily fit into multiple categories.