EDIT: Oops. Should have tested some of these before posting... Seems like it only works for some links but not others. Leaving for future reference.

-----

Windows 64bit: https://downloads.natron.fr/Windows/releases/64bit/files/Nat...

Windows 64bit Online Installer: https://downloads.natron.fr/Windows/releases/64bit/files/Nat...

Windows 64bit zip: https://downloads.natron.fr/Windows/releases/64bit/files/Nat...

Mac: https://downloads.natron.fr/Mac/releases/Natron-2.0.5.dmg

Linux TGZ: https://downloads.natron.fr/Linux/releases/64bit/files/Natro...

Linux Online Install: https://downloads.natron.fr/Linux/releases/64bit/files/Natro...

Linux Portable: https://downloads.natron.fr/Linux/releases/64bit/files/Natro...

Linux RPM: https://downloads.natron.fr/Linux/releases/64bit/files/Natro...

Linux Debian: https://downloads.natron.fr/Linux/releases/64bit/files/natro...

  Note: Future versions - URL is in form 
  http://natron.fr/login?os=Linux&file=https:
  //downloads.natron.fr/Linux/releases/64bit
  /files/Natron-2.0.5-Linux-x86_64bit-portable.tar.xz
  - Remove the http://natron.fr/login?os=Linux&file= 
  part and you are good to go.

The Linux Portable download goes through happily, but every other link redirects to login page. Thanks for the effort though.