A release through Tony's 50/50 Club software followed later. The review in Adventure Probe (as well as comments in an interview with the author) alludes to a planned commercial release by Automata/Interceptor Micros; this seems not to have happened.
The original version of Nythyhel was produced for the Amstrad CPC using GAC.
The C64 version was also produced with GAC. It became particularly well known after its later appearance on the ZZap!64 issue 81 covertape.
An Adventure Probe review mentions that the original Spectrum version was Quilled but that edition is missing from the archives so can't currently be verified.
The revised 50/50 Software release for the ZX Spectrum was produced using the PAW.
This adventure formed the basis of Tony Collins' reworked games Methyhel and Methyhel - The Special Edition.
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excellent!! one of the best i have played for a long time
Glad to hear you enjoyed this one... the remake Methyhel (and the enhanced 128K version) is an even better game, imo. At one point I was discussing working with Tony and a sequel to the game, but sadly Tony left the adventure scene before we made much progress on it.
The c64 version has some graphics, but not a lot.