For those who aren't familiar with passive abilities; generally speaking they are the counterparts to special attacks. God swords for example will have passive abilities, so for every four successful blows one blow will cause any of the options below to happen. E.g. your Armadyl god sword will boost both attack and strength "XX" levels. This implication actually exists with the keris weapon, on rare occasions it will do triple its regular damage due to the fact that it would land a "vital" blow. Right below are the listed passive abilities for each of the god swords, as well as the enchanted exchalibur:
Armadyl god sword: Increases Attack and Strength stats.
Bandos god sword: Decreases targets defense if they are above a certain base defense level.
Saradomin god sword: Heals some of your base life and prayer points.
Zamorak godsword: Stuns your target for "X" amount of seconds.
Enchanted Excalibur: Heals "X" base life points, which will be boosted if the player has completed all of his/her elite Seer's Village tasks.
Jagex plans to carefully watch and gain feedback from the community (us) to see whether or not these passive abilities should be implemented on other existing and future items. Since you couldn't find this post that details passive abilities from head to toe, here's the
official forum post.