Built by the firm's Instagram team, it's billed as a home for "sharing text updates and joining public conversations".

Its release couldn't be more aggressively timed, coming days after another controversial move by Twitter's incendiary owner Elon Musk forced many people to look for an alternative platform.

With a shamelessly similar look and the billions of Mark Zuckerberg behind it, Threads seems well-placed to challenge "the bird app" in a way the likes of Bluesky and Mastodon haven't quite managed - though a significant market remains unconvinced.

Here's everything you need to know.

What is Threads?

Threads is designed first and foremost as a place to share public real-time text updates, just like Twitter.

Indeed, you barely even have to squint, and Threads looks just like Twitter - though it does have a different font.

Posts can be up to 500 characters long and include links, photos, and videos of up to five minutes.

They appear in a timeline, and posts can be liked, reposted, replied to, and shared elsewhere. But posts don't appear chronologically, and there seems to be no way to make it so.

Users will be able to follow celebrities, athletes, and friends, many of whom will have jumped over from Instagram.

It's available on the Apple App Store and Google Play Store.

What do you mean 'jumped over from Instagram'?

Besides the money and influence of Meta itself, the biggest leg-up Threads has on its competitors is it leverages Instagram's already huge user base.

There are more than two billion Instagram accounts, and the same credentials can be used to log in to Threads.

Usernames and verification will carry over, meaning Threads could quickly assemble a huge line-up of celebrities, athletes, politicians, sports clubs, news outlets (including Sky News) and brands that already use Instagram.

It also means you're likely to have more friends and other followers you recognise from Twitter on Threads.

It could very quickly feel a lot livelier than apps like Bluesky and Mastodon, which have grown since Musk's Twitter takeover but still comfortably trail its estimated user base of 360-400 million.

But if you later want to quit Threads, it may not be straightforward. While you can deactivate your account, there appears no way to delete it without deleting your Instagram account too.

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Not joining another platform? Here's why Threads could be the one that catches on
Why are so many apps adopting the same look?

Has anyone famous signed up yet?

Early adopters include accounts for Netflix and Star Wars, chef Gordon Ramsay, pop star Shakira, actor Zac Efron, Formula 1 driver Lando Norris, NBA star Seth Curry, and - naturally - Zuckerberg himself.

Even if you don't follow them, they may show up in your feed if their posts are deemed "recommended content".

It's certainly a smaller line-up to start with than Instagram and Twitter currently have, but could grow fast.

How is Threads handling privacy and safety?

Meta says Threads will have the same features as Instagram in this regard, which may not be enough given that platform regularly faces criticism for its moderation.

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All profiles aged under 18 will be defaulted to private when they join, and anyone can control who can reply to or mention them. Words can also be filtered so you don't see any posts that contain them.

Accounts can be blocked, restricted and reported to Meta's moderation team, and anyone you've blocked on Instagram will automatically be blocked on Threads.

But it's not launching in the EU today over regulatory concerns, believed to be around how much data the app may collect from its users. Meta has fallen foul of European data regulation before - earlier this year it was hit with a record £1bn fine for transferring EU Facebook users' data to the US, where it is subject to fewer privacy protections.

Read more:
Zuckerberg faces long and painful road to metaverse success

Is there anything truly unique about Threads?

Not really to be honest, but there is one interesting decision that could inform how it develops.

Meta says Threads will soon be compatible with ActivityPub - in essence, it's an open social networking protocol allowing different platforms to talk to each other.

It's the same approach taken by upstarts like Mastodon, but more unusual for a major company.

In practice, it would allow you to transfer content between services. So if you've spent the past nine months on Mastodon after leaving Twitter but now want to move to Threads, you could eventually transfer your content.

You could also interact with people on different apps no matter which one you're actively using, with your posts accessible across digital lines. All the while, each platform could still have its own moderation policies.

For many, the biggest issue when it comes to leaving any social media platform is the prospect of abandoning potentially years of content and interactions. Ideally, this decentralised approach could be a solution.