Links for the Mac a few versions back:
https://animationpaper.com/files/a5/AnimationPaper.dmg
https://animationpaper.com/files/a6/AnimationPaper.dmg
https://animationpaper.com/files/a7/AnimationPaper.dmg
https://animationpaper.com/files/a8/AnimationPaper.dmg
They are Alpha 5, 6, 7 and 8 respectively.