Bluesky, one of several alternatives to Twitter that have gained popularity since Elon Musk bought the platform and changed its name to X, now no longer requires an invitation before a user can sign up. Since its launch in 2019 by Twitter co-founder Jack Dorsey, Bluesky had said it was limiting the influx of new users so as not to overload its infrastructure, but announced on Tuesday it was opening sign-ups to all. With access via invitation codes, Bluesky achieved 3 million registrations in its first year and 1.6 million monthly active users as of recently, company boss Jay Graber told the te…