Pity last year's hot initial public offerings -- Dropbox (DBX - Get Report) and Spotify Technology (SPOT - Get Report) .

The pair have been buried by a rush of hot new IPOs such as Zoom Video Communications (ZM) and PagerDuty (PD) . While the latter have soared since their April debuts by 41% and 29%, respectively, Dropbox is down 15% since its offering in March of last year, and Spotify is basically flat with last year's debut, a period over which the Nasdaq Composite has risen 10%.

It's a potent reminder to IPO investors that the bloom does come off the rose in some cases.

However, investors have been taking a second look at the two this year. Spotify's stock has handily beaten the averages, up 27%, year to date. Dropbox is up a tad lower than the Nasdaq this year, up 17%.

The question is what they must do to keep in investors' good graces. What's working and what's not working for the duo is a bit different for each. 

For Dropbox, it's a case of the missing revenue growth, failing to show the top-line-beats that investors in young companies crave. Dropbox has beaten earnings estimates in each of its five quarters as a public company by a healthy margin. Its sales, however, have been basically in line with consensus, at most a couple percent higher than the average estimate in any of those quarters. 

And the rate of growth has cooled, with revenue this year projected to rise by only 18%, down from last year's growth rate of nearly 26%. Sales may rise only 15% next year. Dropbox is seriously in danger of turning out to be a one-hit wonder, a perfectly nice business, but one that has tapped out its addressable market. 

Something else is needed to add new lines of business for Dropbox. On June 11, the company announced what it calls an "integrated workspace." That's a user interface that is designed to hook into document repositories such as Google Docs, but also to connect to other enterprise apps, such as Slack, the collaboration tool sold by the startup of the same name that went public last week.

While Dropbox is trying to absorb these other services, it is likely that Slack (WORK) and other new issues are going to sap the enthusiasm for Dropbox going forward. Estimates for Slack are much higher for this year's revenue growth, at 50%, though Slack is a bit smaller, at perhaps $600 million in revenue this year compared to $1.6 billion projected for Dropbox. 

Having popularized file sharing, Dropbox will remain an important piece of infrastructure, but it is not the kind of go-to app that Slack is perceived to be, as far as where employees spend their time. The fact that Dropbox doesn't keep track of the "retention" rate of users, or the degree to which they renew their subscriptions to its service, is telling.

Retention rate is one of Wall Street's favorite metrics to track companies' progress in enterprise software. At this point, Dropbox is out of step with the rest of the enterprise software crowd, including Slack and Zoom, and others, and likely to continue to merely tread the market average.

Spotify is a bit of a different case, as its revenue growth is accelerating to perhaps 27% this year, or $7.7 billion, up from a rate of growth of 20% last year. The stock is cheap as a multiple of revenue of about 3.5 times, and though Spotify is still losing money -- it may have negative Ebitda of $131 million this year -- the losses are narrowing. It's possible the company will turn a profit come 2021, which would likely add to its appeal.  

The number of users, on average, each month, continues to rise in a healthy fashion for Spotify. At the end of the March quarter, it was a total of 217 million, which was up 26% from the prior-year period. 

That growth in users is everything: Spotify wants to avoid the slowdown that happened at Twitter last year, when it topped out at 330 million monthly average users and then actually declined in 2018. As long as Spotify can keep bringing in users, their service is perceived as a relatively stable operation that will produce meaningful cash flow at some point in the future. That hardly sounds like a scintillating business, but in internet terms, that's success.

Dropbox will next report results on August 8, while Spotify reports July 25.

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Tiernan Ray neither trades nor owns any shares of any companies mentioned in this article.