Identify a problem. Figure out a smart way to address said problem. Make boatloads of money. Sounds simple enough, right? 

Of course, it's never that simple--particularly the part about finding a smart and lucrative solution to a gnarly problem. If you need a little inspiration, take a look at some of the most innovative businesses on Inc.'s annual list of the fastest-growing private companies in the U.S. The list below showcases some of this year's honorees that came up with brilliant business models. In some cases, these businesses are attacking problems you probably didn't even know existed, like how hard it can be to find those tasty cookies you ate in Germany. 

Here are the most innovative business models of the 2019 Inc. 5000, presented in no particular order.

1. Buy now, pay later.

With Perpay, consumers can take their products home before they pay for them. A survey earlier this year found that 40 percent of American adults wouldn't be able to afford an unexpected $400 expense. Perpay, which landed the No. 5 slot on the 2019 Inc. 5000, caters to people who don't have all the cash upfront to purchase what they need. Perpay buys goods wholesale--everything from fridges and TVs to car tires and strollers--then resells them at an upcharge, letting customers pay in installments deducted directly from their paychecks. The model seems to be working: The company has served more than 1 million customers since its 2014 founding and generated $22.5 million in revenue last year.

2. In-store rewards, online.

Think extreme couponing, but with a mobile app rather than paper and scissors. Ibotta, No. 699 on this year's list, lets users select cashback offers; then, if they make a purchase in-store, they can upload their receipt to get up to a 10 percent rebate. The company has secured partnerships with more than 1,500 retailers, including Macy's, Kohl's, Lowe's, Home Depot, Bed Bath & Beyond, Uber, Expedia, the Gap, and Etsy. Ibotta's app has been downloaded more than 30 million times, and the company pulled in $157 million in revenue in 2018.

3. Portable chargers that never die. 

There are a lot of portable charging blocks on the market, but Tricopian's $25 Fuel Rod comes with a unique twist: You can swap it for a fully charged one at one of the company's kiosks. Tricopian has placed its machines in heavily trafficked areas including airports, malls, and theme parks--SeaWorld, Universal Studios, the San Diego Zoo, etc.--and there's no limit to the number of swaps you make. Last year, Tricopian earned $7 million in revenue, good for No. 178 on the Inc. 5000 list. 

4. Financial aid made easy.

Applying for financial aid is confusing--and for 40 percent of admitted low-income students, not getting it means they don't end up enrolling at all. CampusLogic, No. 175 on this year's list, built a platform that simplifies the process of applying for financial aid, helping students find scholarships and funding opportunities for which they're eligible, alerting them of deadlines, and automating simple but time-consuming steps. The B2B company, which made $14.2 million in revenue last year, sells its software directly to universities, which incorporate the platform into their application processes. 

5. Sophisticated snack subscriptions.

Your pantry is about to get more cultured. Universal Yums, No. 190 on this year's list, ships its subscribers a box of snacks from a different country every four weeks. Each month focuses on a different nation, and many of the snacks--which range from sweet (Korean chocolate pies) to salty (Thai spicy fried seaweed)--can't otherwise be found in the United States. Each box comes with a booklet of trivia, history, games, and recipes from that month's country. The business of snacking was lucrative for the startup last year, as it brought in $12.7 million in revenue.

6. Co-signing leases.

Getting approved for a lease can be a major issue for people with bad credit. Liberty Rent Guarantee, No. 336 on this year's list, acts as a co-signer for applicants who are having trouble securing a lease. In exchange for one month's rent, the company agrees to be on the hook for up to six months if a renter breaks a lease. That's often all the assurance a landlord needs. The company has gotten more than 8,000 leases approved since its 2014 founding and made $2.2 million in revenue last year.

7. Engagement ring tryouts.

No. 18 on this year's list, With Clarity, takes some of the stress out of buying an engagement ring. The online jewelry retailer lets potential customers build their own rings online, then 3-D prints and ships replicas to try on at home--for no charge. Once a user is sure they like it, they can buy the real thing, including choosing from a selection of tens of thousands of conflict-free diamonds. The startup, founded by a couple shortly after their own engagement, pulled in $19 million in revenue in 2018.