This year marks the first time the four-day event, which grew out of anti-globalization protests in the late 1990s, is being held in an Arab country, Tunisia Live reported.
The forum began with a Tuesday afternoon march by participants sporting banners, flags and even balloons as they chanted social justice slogans such as "down with dictatorships" and "freedom to the people."
"The revolution is far from being over," said Danny from the Spanish 15-M Movement. "It hasn't achieved its goals yet. Tunisians must go on with the struggle."
During the forum participants will attend hundreds of workshops, debates and concerts on the campus of Tunis El Manar University.
High on the agenda are tax justice and campaign against debt, organizers said.