Our website provided a free download of NasuToArena 1.0 for Mac. The program lies within System Tools, more precisely File Managers.
From the developer:
NasuToArena is a HC Stack converting "Nasu" (NIFTY Log browser) files to mbox format files for ARENA (and Eudora).
You may want to check out more Mac applications, such as Open.nuke folder, d-d Zone or Butterflyzer, which might be similar to NasuToArena.