Well, Amazon has taken a page out of Apple’s playbook and fused software with hardware here.
Skype has bots now, and needs to add Cortana to be comparable on the Alexa front. But Skype doesn’t have its own branded physical form factor.
Google Assistant is close, but relies on third party screens via Chromecast right now (that may change at I/O).
Alexa and Siri are of course competitors, and we’re likely to see Apple put out their own FaceTime device with Siri built in at WWDC this year, but Siri sucks in comparison with Alexa (so far).
Ultimately, Microsoft, Google, Apple, and Amazon are all going to compete to own the post-personal-computing/home device market, but Amazon has a clear lead, and several advantages over the others. It’s true that the Echo Show is positioning itself as a device for making video calls, but that’s just, again, what’s being emphasized. It’s the ecosystem springing up around Alexa that makes it so interesting and promising, relative to the other platforms.