From 1st Evening High School of Piraeus
Team members: Anthi Tournatzi, Ioannis Bazaios, Hrakleia Tournatzi, Athanasia Kotzamani.

Here we present some categories of social networks. For each category we listed some social networks. It is obvious that there exist so many other social networks which increased rapidly as it listed to the reference link.

Education
Academia.edu (for academics/researchers)
aNobii (books)
Bussu (Language learning community)
Classmates.com (School, college)
Epernicus (for research scientists)
Livemocha (Online language learning)
Shelfari (books)
weRead (books)

Travel

Passportstamp (travel)
TravBuddy.com (travel)
Travellerspoint (travel)
WAYN (travel)
CouchSurfing  (between travelers and the local communities they visit)

Music

Buzznet (Music and pop-culture)
Gogoyoko (Fair play in Music)
Last.fm (music)
MOG (music)
Partyflock (Dutch virtual community for music)
Playlist.com (General, Music)
SoundCloud (Repository of original music pieces)

Movies

FilmAffinity (Movies and TV Series)
Flixster (Movies)
MUBI (Auteur cinema)

Games

GamerDNA (Computer and video games)
Lifeknot (hobbies)
Playfire (Computer and video games)
Raptr (Video games)
Wakoopa (For computer fans that want to discover new software and games)
Gaia Online (Anime and games)

Photography

Flickr (Photo sharing)
Fotki (Photo sharing)
Fotolog (Photoblogging)
Gather.com (picture sharing)
My Opera (Photo sharing)
DailyBooth (Photo-blogging site)

For particular countries
Grono.net  (Poland)
iWiW (Hungary)
LunarStorm (Sweden)
Mixi (Japan)
Nexopia (Canada)
IRC-Galleria (Finland)

General

Bebo
Bolt.com
Cloob
Cyworld
Draugiem.lv
Facebook
Google +
Google Buzz
Makeoutclub
Meetin
Myspace
myYearbook
Tagged
Taringa!
Wer-kennt-wen

Reference

http://en.wikipedia.org/wiki/List_of_social_networking_websites