The "8sk" suffix often appears in community-modified versions of emulators, sometimes associated with specific "skins," "sketches," or developer handles. Since I cannot open the file directly, here is the general context of what a "Nester" zip file typically contains:
Are you trying to with this version of Nester, or Nester8sk_Old.zip
Supporting files required for the emulator to interface with your hardware. sometimes associated with specific "skins
A file like Nester.exe used to run NES games on a PC. Nester8sk_Old.zip