Meta's Threads app debuted a day earlier than expected, offering billions of users with an alternative to Twitter amid growing frustration with the Elon Musk-owned social media service. 

Threads had been slated to be released at 10 a.m. Eastern Time on July 6, but the company on Wednesday pushed forward its countdown clock to 7 p.m. Eastern time on July 5. 

Within hours, 10 million people had signed up for the service, according to Meta CEO Mark Zuckerberg.  By Thursday morning more than 20 million had signed up, according to NBC News, which cited the number of Threads badges on Instagram users' accounts.

Threads, which looks similar to Twitter, lets users post messages, reply to other users, and like or repost messages. The service also lets users of Meta-owned Instagram follow the same accounts on Threads, which could help people add followers.

"Our vision is to take the best parts of Instagram and create a new experience for text, ideas and discussing what's on your mind," Meta founder and CEO Mark Zuckerberg said in an Instagram post after Threads was made available for download. "I think the world needs this kind of friendly community, and I'm grateful to all of you who are part of Threads from day one."

However, there are some differences between Threads and Twitter, including that Threads doesn't use hashtags, a popular way on Twitter and Instagram to quickly find topics of interest. There's also no option to directly message other users on Threads, unlike on Twitter and Instagram.

In the days leading up to Threads' release, some people on social media referred to it as a "Twitter killer" because of the expectation that some users of the rival platform will jump ship in favor of the new app. Some Twitter users have expressed frustration with recent changes instituted by CEO Elon Musk, who this week throttled the number of tweets that nonpaying users are able to view per day. 

Twitter has also seen a spike in hate speech since Musk bought the platform last year.

"Meta is banking on a moment in time amidst peak Twitter frustration," noted Mike Proulx, vice president at tech research company Forrester, in an email. 

Here's what to know about Threads.

What is Instagram Threads?

Proulx described Threads, which is billed as an Instagram app, as "another copycat move" from Meta, which has sought to introduce other services in the past that mimic other standalone tech tools. They include Slingshot, an instant-messaging app, and IGTV, which was a video service from Instagram. 

In this case, Meta bills Threads as a place where you can "follow and connect directly with your favorite creators and others who love the same things." In other words, sort of like Twitter, but perhaps with more focus on the creators and influencers who are popular on Instagram. 

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When will Threads launch?

The service went live Wednesday evening. The app is available in Apple's App Store. It's also available in the Google Play store.

Are there more Twitter alternatives? 

Yes, there are several, with Bluesky in particular receiving considerable attention. The service, which is backed by Twitter co-founder Jack Dorsey, remains in its testing phase and not fully open to the public. Entry to the invite-only beta can be hard to come by. 

Meta will have to compete with a flood of other Twitter alternatives, including Mastodon, Post.News and Hive, Proulx noted. Thread "only serves to fracture the Twitter alternative-seeking user base," he noted.