Most intriguingly, Simple isn't just targeting married couples and longterm couples. Any two people can create a shared account for managing their finances, which could be useful for roommates or friends traveling together. Both customers will also get individual accounts from Simple, which they can swap between the joint account easily in the company's apps.

As you'd expect, you can also sign up for Simple Shared accounts easily online. That's a big change from traditional banks, which typically require you and your partner to appear, fill out lots of forms, and prove your relationship.

Simple is keeping its shared accounts in beta testing for now, and it plans to have an official launch once it sees how people use the accounts. That might sound worrisome, but it makes sense for Simple to take things slow, after it faced some serious technical issues years ago which required a hefty infrastructure revamp. The company eventually bounced back, but it seems to have learned its lesson about moving too quickly without enough testing.