Old-School Essentials Advanced Fantasy and Pugmire come to mind. I expect it would probably require a court to determine whether the OGL’s definition of OGC does include the mechanics regardless of the Product Identity designation. The ORC License appears to be trying to be much more explicit about the intent.
From the OSE
Player’s Tome:
All artwork, logos, and presentation are product identity. The names “Necrotic Gnome” and “Old-School Essentials” are product identity. All text and tables not declared as Open Game Content are product identity.
This is the designation, which is almost all stuff from Classic Fantasy (e.g., barbarian is not so designated) plus Secondary Skills:
All text and tables in the following sections are Open Game Content: Advancement, Vehicles and Mounts, Cleric Spells, Magic-User Spells, Hired Help, Strongholds.
All text and tables in the following subsections of the Player Characters section are Open Game Content: Game Statistics, Creating a Character: Basic Method, Ability Scores, Alignment, Languages.
The table of Secondary Skills (p25) is Open Game Content.
All text and tables in the following subsections of the Character Classes section are Open Game Content: cleric, dwarf, elf, fighter, halfling, magic-user, thief.
All text and tables in the following subsections of the Equipment section are Open Game Content: Adventuring Gear, Weapons and Armour.
All text and tables in the following subsections of the Magic section are Open Game Content: Spells, Spell Books (excluding the Advanced Spell Book Rules section), Magical Research, Cleric Spell List, Magic-User
Spell List.
All text and tables in the following subsections of the Adventuring
section are Open Game Content: Party Organisation, Time, Weight,
and Movement, Ability Checks, Saving Throws, Damage, Healing, and Death (excluding the Returning from Death section), Hazards and Challenges, Dungeon Adventuring, Wilderness Adventuring, Waterborne Adventuring, Encounters, Evasion and Pursuit, Combat, Other Combat Issues (excluding the Attacking with Two Weapons, Charging into Melee, Missile Attacks on Targets in Melee, Parrying, and Splash Weapons sections), Morale, Combat Tables.
From
Pugmire Core Rulebook:
All mechanics are declared Product Identity, unless covered by a different license.