For the original hobby niche of small electronic projects where a microcrontroller with wifi will suffice, the ESP8266 / ESP32 have been quickly overtaking the pi zero. Of course it's not really comparable and there is the Rpi Pico as a competitor but I find the ESP32 much easier to work with. It's also much cheaper (not to mention the 8266)

For heavier usecases that really there isn't as much of an alternative. Many other boards like the pine64, beagle and orangepi, but their ecosystem lacks sophistication.