X-Alternative Bluesky is now open to everyone. The first three million users were only given access to Bluesky through invitations.
Now you can simply register with an email address. The user interface is reminiscent of the earlier Twitter, the focus is on short texts, images and links. Timelines sorted according to personal preferences. Currently available are, among other things, a “Science” feed, which only shows content from people working in science, and a feed only for cat pictures.