Jack Dorsey’s new Twitter alternative, Bluesky, is now available in closed beta on the App Store. The invite-only app could soon join a crowded field of budding Twitter competitors, including Mastodon.

Interested users can submit their email addresses to join the waitlist. The Bluesky app reportedly borrows heavily from Twitter. However, it includes minor differences like “What’s up?” in place of “What’s happening?” along with a simplified process of creating a post (which can also include photos) by selecting a plus button. Otherwise, it has familiar features like searching for and following users and viewing their posts on a Home timeline.