Originally, Tween was developed for heavy users. For this reason, Tween is a Twitter client with various functions. There are web mode and API mode, and users can switch between modes. Web mode allows users to avoid API limit's operation.
The first beta version was released at Hatena Diary on Nov. 21, 2007. Originally web mode was an only way to get data, then API mode was implemented. 0.7.7.7 was released on Oct. 2, 2009, and API mode was set as default. 126.96.36.199 or later became Proprietary software.