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 Butterflyzer or FileVaporizer, which might be similar to NasuToArena.