This first international expansion market represents the company's continued commitment to helping the next generation of investors chart a path to financial freedom by eliminating the barriers that have traditionally made starting to invest so daunting.

"We built Acorns specifically to address the needs and preferences of millennials," said Walter Cruttenden, co-founder and CEO of Acorns. "Our mobile-first approach is well-suited to today's on-the-go lifestyle, and features such as round-ups on everyday purchases encourage small financial decisions that add up to a big difference in personal wealth over the long term."

Mobile usage in Australia is pervasive, with smartphone owners typically spending 35 hours per month consuming content and using apps on their devices, according to an August 2015 report from Nielsen Mobile Ratings and IAB Australia.

Early interest in Acorns among young Aussies underscores the hunger for a better, more convenient way to incorporate saving and investing into their everyday lives. More than 26,000 people have already signed up for a waiting list to download the app, which becomes available in the App Store and on Google Play today.

Acorns Australia is a joint venture between Acorns Grow Inc. of the USA and Instreet Investment Limited, based in Sydney. The joint venture was established in March 2015. Acorns Grow Australia Limited will promote, distribute and provide fund manager services to the Acorns app in Australia. Instreet has appointed Acorns Grow Australia Limited as an authorised representative of its Australian Financial Services License.

"Australia is an important first step in our international expansion plans," said Cruttenden. "We've had inbound interest from around the world and have built the infrastructure necessary to grow our global footprint. This joint venture is a great milestone as we open up opportunities for young people to take more control over their financial future."

In the U.S., Acorns has rapidly gained traction with millennials. More than 700,000 investment accounts have been opened in 16 months -- nearly 70% of them by investors ages 18 to 34.