OSE Encounter Activity Tables     Any original/official source
Pathfinder 2e Bestiary 1     Pathfinder original/official source
Monster Manual     D&D 4e (no source link)
Scruffy Grognard's Monstrous Manual     D&D 2e (no source link)
Critters, Creatures, & Denizens     Dungeon Crawl Classics (no source link)
Harnmaster 5e     Harnmaster (no source link)