For the most part, I resist the “best” this or that lists pitched my way by all manner of market research and technology companies at the end of the year. Still, I was intrigued by one flung my way this week by Okta, a software purveyor that created a system that centralizes sign-on privileges for cloud applications.

The list reflects log-in data from the several thousand businesses that use Okta’s access management technology, including MGM Resorts, Chiquita Brands, FICO, and Western Union. Right now, it supports more than 4,000 software applications sold as a service. One of the more intriguing lists Okta cooked up based on usage trends over the past year was a ranking of the 15 fastest-growing apps. The top app in terms of adoption growth was Slack’s business messaging service. (Just in case you’re wondering, Slack now boasts more than 2 million registered users.)

I’m not surprised either, although many of the other software companies near the top of the list are far less familiar.

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Ever hear of New York-based Greenhouse? It sells a recruiting management service used by the likes of eyeglass retailer Warby Parker, social network Pinterest, and hospitality company Airbnb. The company raised a $35 million round in venture funding last August, barely five months after its previous infusion. It’s not the most widely used service supported by Okta; that honor goes to Jobvite, an analytic-driven recruiting software.

What about Envoy? Its mobile application helps Box, GoPro, and Yahoo manage the comings-and-goings of office visitors. The company’s $15 million Series A round last June was led by Andreessen Horowitz. Another thing in the San Francisco-based startup’s favor: it is part of Slack’s new certified application network.

You should also remember this name, Zapier, which hails from Mountain View, Calif. Its mission is to help companies create connections between different cloud business applications. Why does this matter? Zapier’s Clio software makes the process of sharing data simpler. So far, it’s only disclosed outside funding of $1.2 million in its seed round.

Incidentally, the top three fastest-growing categories in Okta’s cloud application network were recruiting services, project management, and business messaging. I’ll be watching its growth list closely.