Campaigning groups preparing for the European Social Forum in October have launched an alternative website after months of clashes with the Greater London Authority over control and planning of the event.
Critics have complained that the official GLA-constructed website, www.fse-esf.org, is not sufficiently interactive and does not allow democratic participation in decision making.
The alternative site, esf2004.net, claims to be an open, democratic forum "to facilitate communication and networking between all interested groups and individuals".
The GLA said it would launch an upgraded version of the official site next week to make it more interactive.
Tensions between the GLA and left-wing activists have developed since Mayor Ken Livingstone backed the plan to hold the forum in the capital.
The GLA is backing the event with £250,000, with a similar sum coming from the trade unions.