Pathfinder 1e Bestiary 2     Pathfinder original/official source
Forgotten Foes     Pathfinder original/official source
Untamed Wilds     D&D 5e original/official source
Critter Compendium     D&D 5e original/official source
Monster-A-Day     D&D 5e original/official source
Monster Manual 2     D&D 4e (no source link)