Since its IPO debut in September, some investors have flocked to the cloud data company Snowflake (NYSE:SNOW). And while the company could make a good long-term investment, the rapid rise in its share price has made the stock expensive, trading at 193 times the company's price-to-sales.

Investors looking for fast-growing tech stocks without the nosebleed valuations should take a closer look at PayPal (NASDAQ:PYPL) and Appian (NASDAQ:APPN). Here's why.

1. PayPal: A leader in digital payments

There's nothing wrong with investing in high-flying tech stocks, but sometimes you can find a better bet by looking to companies with proven track records. PayPal is a leader in the digital payments market, it continues to add new users, and its share price has climbed 120% year to date. 

A person pointing to a tablet.

Image source: Getty Images.

PayPal proves that just because you're an established leader in a market doesn't mean you can't keep growing quickly and delivering strong returns for investors. In the most recent quarter, PayPal's sales jumped 25%, total payment volume on the company's platform spiked 36%, and PayPal added 15.2 million net new active accounts (hitting 361 million). Additionally, non-GAAP earnings per share spiked 41% to $1.07. 

The company isn't satisfied with that growth, though, and it's been rolling out new features to add new customers and retain its current ones. One such example is the company's recent expansion of its buy-now-and-pay-later service, which allows customers to make interest-free installment payments and keeps PayPal users more engaged with its payment platform.

Additionally, PayPal's rapidly growing Venmo app -- for peer-to-peer payments -- has continued to expand. Users can now use the app to buy things from merchants. In the third quarter, Venmo's total payment volume (TPV) was up 41% from the year-ago quarter. 

PayPal should continue to benefit in this market as digital payments grow from a current market size of $910 billion to an estimated $1.5 trillion by 2024, according to a Statista analysis. 

2. Appian: It's only an app away 

Apps are everywhere these days. I signed up to give blood last week, and guess what, there's even an app for that. Apple's App Store now has 1.96 million of them, and Google's Play Store has an astonishing 2.9 million.

What does that have to do with Appian? The company created a low-code process for creating apps, meaning that users don't need to know how to write code to build their apps. Creating an easier way to build apps has been a smashing success for Appian, and in the most recent quarter, the company's cloud subscription sales increased by 40%. And management estimates that full-year 2020 cloud subscription revenue will pop 34% year over year.

But can Appian keep the momentum going? Most likely. The mobile app market was worth $106 billion in 2018 and will reach an estimated $407 billion by 2026, according to an Allied Market Research study. There aren't enough developers around to make all of the apps that companies need these days, and some will turn to Appian's platform to do it for them.

In fact, a lot of them already have. The company said in its recent earnings call that "Global organizations depend on our technology, including nine of the top 10 life sciences firms, six of the top 10 asset managers, five of the top 10 banks, and more than 100 government groups."

Set it and (almost) forget it

Building wealth involves finding great companies, buying their stock, and then holding onto those stocks for years, not quarters. Appian and PayPal could see their share prices spike in 2021, just like they did this year, but investors should remember that investing in these companies will likely bring the biggest gains by holding onto them for at least the next three to five years.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.