The Council of Pisa is not one of the 21 councils recognized by the Roman Catholic Church today. It was held in 1409 in an attempt to end the Western Schism, sometimes called the Papal Schism. This schism lasted from 1378 to 1417 some thirty years. By 1409 none of the means employed to bring it to an end had been successful. Most say that compromise or arbitral agreement between the parties had never been seriously attempted largely because of the obstinacy of the rival popes, both equally convinced of their rights. The interference of princes and armies did not help either.  

The council proposed deposing both Benedict XIII (Avignon) and Gregory XII (Rome). Instead of ending the Western Schism, the Council elected a third papal claimant, Alexander V, He reigned from June 26, 1409, to his death in 1410.  He was succeeded by John XXIII who reigned from 1410-1415.  Both Alexander V and this John XXIII are considered antipopes by the Roman Church today.  

The chart below shows the claimants to the papal throne

 Rome Avignon  Pisa  Comment 
1316-1334 John XXII  
Moved seat of Papacy from Avignon back to Rome
1378-1389 Urban VI 1378–1394 Clement VII The French king, Charles V, had recommended that the cardinals assembled at Anagni and Fondi revolt against Urban VI 
1389-1404 Boniface IX
1394–1423 Benedict XIII  
1404-1406 Innocent VII  
1406-1415  Gregory XII  1409–1410 Alexander V The cardinals of the reigning pontiffs were dissatisfied, both with the lack of strong leadership and nepotism of Gregory XII and the obstinacy and bad will of Benedict XIII so they conviened the council of Pisa and tried to depose both Gregory and Benedict. They elected Alender V  as an alternative. That did not solve the ptoblem as it just created a third claimant.
1410–1415 John XXIII  
1417-1431 Martin V      
 1/27/14 1/27/14 1/27/15