Of course the most sincere form of flattery is imitation and indeed, Twitter has a veritable smörgåsbord of rip-offs and imitators, primarily of the non-English variety. (Originally reported by Tim and Rabble). And now picked up by Wired and Techcrunch.

March of the Clones

By country (incl. supported language versions)

China

• Komoo (Chinese)

Germany

• 1you (German)
• Baluuu (German)
• Das Beep (German)
• Dukudu (German) (auctioned off on eBay, acquired by allesklar.de for EUR 43,208)
• Faybl (German)
• Frazr (German, French)
• Plappadu (German)
• Sloggen (German)
• Texteln (German) (auctioned off on eBay, acquired by S² Media GmbH & Co. KG for EUR 11,161)
• Wamadu (German)
• Brabblr

Hungary

• Turul Twitter

France

• noumba (French)
• Yelago (French)

Korea

• me2DAY (Korean) (closed beta) -- Source: itMilk IST Blog: Korean Twitter Clone: Me2day

Singapore

• Tiish

Netherlands

• Numpa (Dutch)

Poland

• Robisz.pl (Polish) -- Source: Badly copied idea is worse than no idea II.

Spain

• Jisko (spanish) (Closed Beta) -- Open Source (AGPL)

Taiwan

• Buboo (Traditional Chinese)

Thailand

• NokNok (Thai)
• Kapook Jeawjaw (Thai)

USA

• Bebo (English) -- Source: Mashable: Bebo Clones Twitter, Blatantly
• CubeVoice
• Facebook (English) (source needed)
• Skittr (English) -- Note: Skittr is example code that is part of the lift web framework.)
• Zannel
• Kwippy

Other projects

• Shopalize - What did you buy today?
• Laconica - open source microblogging tool
  • Identica - reference implementation of Laconica
  • Lareta - Spanish language installation of Laconica