It also reminds me of a similar option, the Jupiter Ace [1] which ran FORTH natively. The co-founders worked on the speccy and certainly borrowed some design as

It also reminds me of a similar option, the Jupiter Ace [1] which ran FORTH natively. The co-founders worked on the speccy and certainly borrowed some design aspects from the ZX81 (had a better keyboard though - ha!) The manual was great for its time, a little dated now but still a decent read [2]. It was reprinted in 2018 and still available [3]. [1] https://en.wikipedia.org/wiki/Jupiter_Ace https://en.wikipedia.org/wiki/Jupiter_Ace [2] https://archive.org/details/vickers_steven_jupiter_ace_4000_forth_programming/mode/2up https://archive.org/details/vickers_steven_jupiter_ace_4000_... [3] https://www.amazon.com/Jupiter-ACE-Manual-Anniversary-Programming/dp/1785387294 https://www.amazon.com/Jupiter-ACE-Manual-Anniversary-Progra...