Just a Public Service Announcement, subject to changes in KTOS, etc etc.
This thread lists skill usage availability of other classes during Rune of Giants. If some listed skills are available, you can assume the unlisted skills are not available, and vice versa.
All Wizard skills are available during Rune of Giants.
Shadowmancer - Shadow Pool, Hallucination, Shadow Fetter available
Warlock - Ghastly Trail available
Pyromancer - Enchant Fire available
Elementalist - Stone Curse Available
Sage - Portal Shop available
Featherfoot - Levitation available, Blood Curse not available
— I’m assuming Blood Curse is only available during Levitation, or I’m doing something wrong
Enchanter - Craft Spellbook, Enchant Lightning, Empowering available
Chronomancer - Pass not available
Linker - Spirit Shock not available
Thaumaturge - Reversi not available
Pyschokino - No skills available
Cryomancer - No skills available
Sorcerer - No skills available