Channel4 itself, although over 3 years old, has not really much of a significant history. The website originally was an idea of 'squeeks', the administrator of the site. The concept of anonymous BBS's has been around on the internet for a long time, however in May 1999 a Japanese university student, Hiroyuki Nishimura started 2channel, which is arguably the largest BBS in the world, reaching out to millions of Japanese users. It's sucess is attributed to it's early start in the social adoption of the Internet, and a few surges in popularity and awareness, caused in part by specific events and media coverage.
Channel4 was started in November 2004, originally as a bit of an experiment, completely un-aware of world2ch and the demise it had suffered. However, as time and a somewhat stable user base has emerged, the idea of it being an "experiment" was abandoned, and today it's run not for profit or any gains, just for a bit of fun. Over time, users have helped create tens of thousands of posts and a community of users, quite a few who have come and gone over time.
English offsprings have yet to show the sucess that 2channel has today. Part of the reason is due to timing, but more noticably, due to different attitudes by western societies, which tend to be more self-orientated in nature in comparison to more individual yet collective societies.