Of course there was the 'holy trinity' of the TRS-80, PET and Apple II in 1977. But even with Sinclair, the ZX80 / ZX81 came before the Spectrum.

https://cybernews.com/editorial/the-1977-trinity-and-other-e...

And before the Apple II, the Apple I and Kim-I. As a sokoban lover I'd love one for the Apple I or the Kim-I over serial, but the 1K RAM limit looks tiny. But you can always create several tapes/ROMs with different level sets...