In a comment on the death of G+, elisteran brought up something that long annoyed me out of all proportion with its actual significance. What do you call a collection of servers communicating through NNTP? You don't call them "INN", you call them "Usenet". The system of hosts communicating through SMTP is not called "Exim", it is called "e-mail". But when someone wants to escape G+, they often consider "Mastodon". Isn't it odd?
Mastodon is merely an implementation of Fediverse. As it happens, only one of my Fediverse channels runs on Mastodon (the Japanese language one at Pawoo). Main one still uses Gnusocial, the anime one was on Gnusocial and migrated to Pleroma a few months ago. All of them are communicating using the OStatus protocol, although a movement is afoot to switch to ActivityPub. Hopefully it's more successful than the migration from RSS to Atom was.
Yet, I noticed that a lot of people fall to the idea that Mastodon is an exclusive brand. Rarely one has to know or care what MTA someone else uses. Microsoft was somewhat successful in establishing Outlook as such a powerful brand to the exclusion of the compatible e-mail software. The maintainer of Mastodon is doing his hardest to present it as a similar brand, and regrettably, he's very successful at that.
I guess what really drives me mad about this is how Eugen uses his mindshare advanage to drive protocol extensions. All of Fediverse implementations generaly communicate freely with one another, but as Pleroma and Mastodon develop, they gradually leave Gnusocial behind in features. In particular, Eugen found a loophole in the protocol, which allows to attach pictures without using up the space in the message for the URL. When Gnusocial displays a message with attachment, it only displays the text, not the picture. This acutally used to be a server setting, in case you want to safe your instance from NSFW imagery and save a little bandwidth. But these days pictures are so prevalent, that it's pretty much impossible to live without receiving them. In this, Eugen has completed the "extend" phase and is moving onto "extinguish".
I'm not sure if this a lost cause by now. At least I hope that members of my social circle migrate to Fediverse in general, and not to Mastodon from the outset. Of course, the implementation does matter when they make choices. As I mentioned, for anything but Linux discussions, pictures are essential, so one cannot reasonably use a Gnusocial instance for anime, for example. And, I can see some users liking Mastodon's UI. And, Mastodon's native app support is better (or not). So yes, by all means, if you want to install Mastodon, or join an instance that's running Mastodon, be my guest. Just realize that Mastodon is an implementation of Fediverse and not the Fediverse itself.
UPDATE 2019/02/11: Chris finds a silver lining.