Voadam
Legend
I know Bastion Press' Legacies uses a ToH monster in one of its adventures. I know one of the Warlords of Arena (in Bastion's Oathbound Arena) uses an OGC race and prestige class. I believe Goodman games has used ToH monsters in some of their DCC adventure modules as well.
The EnPublishing/Ambient Necromancy book Gar Udock has OGC stuff.
I know Green Ronin's Witch's Handbook adapted the OGC ritual system from Relics and Rituals, and Maladin's Gate added some new rituals in St. John's College of Abjuration.
WotC used OGC stuff in MM2 and significantly in Unearthed Arcana.
I believe a bunch of the "built from the ground up to meet a specific style" worldbook/alt PHs use some OGC stuff.
There are the compilation books that use tons of OGC, see various ones by XRP (monster geographica for the win!), Green Ronin (pocket grimoire, etc.), FFE (various), and Mongoose (various).
The EnPublishing/Ambient Necromancy book Gar Udock has OGC stuff.
I know Green Ronin's Witch's Handbook adapted the OGC ritual system from Relics and Rituals, and Maladin's Gate added some new rituals in St. John's College of Abjuration.
WotC used OGC stuff in MM2 and significantly in Unearthed Arcana.
I believe a bunch of the "built from the ground up to meet a specific style" worldbook/alt PHs use some OGC stuff.
There are the compilation books that use tons of OGC, see various ones by XRP (monster geographica for the win!), Green Ronin (pocket grimoire, etc.), FFE (various), and Mongoose (various).