Bill.com, a web-based provider of  bill payment, invoicing, and cash management tools for businesses, announced the opening of its platform to API access today.

Expanded API access is all the rage in fintech lately, with Intuit, Capital One, Lemon, and LevelUp all introducing expanded API applications recently. Bill.com’s API will allow its customers to create their own custom applications that fit their specific business needs.

The services that end up being built around Bill.com may offer innovative ideas to Bill.com itself, and allow the banks that tap Bill.com’s API to offer more value to customers.

Bill.com is known for its payments processing solutions, which allow FIs to offer businesses the ability to send and receive payments. Bill.com also offers a  suite of tools for small-to-medium-sized businesses, such as cash flow management, document management, and synchronization with most popular accounting software packages.

API evangelists maintain that APIs fulfill the early promise of the web by allowing websites (or databases) to truly interact with one another to produce something bigger and better. Google, PayPal, and social media sites lead the way in allowing other sites to use their information to create mash-ups.

The first bank to hook into Bill.com’s API was the forward-thinking Mercantile Bank of Michigan, according to MercBank CIO John Schulte. Bill.com itself counts more than 100,000 users of its services. Bill.com’s API was first appeared “in the wild” on May 21, 2010, according to Programmable Web, a site that tracks APIs and mash-ups.