A new study of the most popular apps in the U.S. provides key takeaways for investors following tech juggernauts Apple (NASDAQ:AAPL), Facebook (NASDAQ:FB), and Alphabet (NASDAQ:GOOGL) (NASDAQ:GOOG) (formerly Google). Here are four observations.

1. Facebook and Google dominate apps
While Apple-branded hardware represents the largest slice of U.S. smartphone sales, along with the tech giant also dominating global profits derived in the segment, Google and Facebook are the clear leaders when it comes to apps.

Of the top 10 apps measured by Nielsen, the top eight were all Facebook and Google apps.

  1. Facebook
  2. YouTube
  3. Facebook Messenger
  4. Google Search
  5. Google Play
  6. Google Maps
  7. Gmail
  8. Instagram
  9. Apple Music
  10. Maps

Even more, Facebook and Google's apps represented an impressive 88% of the total monthly unique visitors measured between all the apps.

2. Facebook's lead won't be easily trumped
's (NASDAQ:FB) native app is the most popular app in the U.S., according to data from Nielsen. In the study, which ranks apps by average monthly unique visitors between January and October, Facebook's app was well ahead of second-place YouTube. Facebook boasted an average of 126.7 million unique users a month, according to Nielsen. Alphabet's YouTube had 97.6 million average unique visitors a month.

Even more, Facebook is growing faster than second-place YouTube, according to Nielson. Facebook's average unique visitors were up 8% compared to the year-ago period and YouTube's were up 5%.

3. The Facebook and Messenger split was a huge success
When Facebook decided in 2014 to split Facebook and its messaging service into two different apps, many users were upset. But, heading into 2016, the discontent seems all but forgotten. Even more, Facebook's strategic decision to split itself up has panned out extremely well. Together, Facebook and Messenger now represent two of the top three apps in the U.S., according to Nielsen.

Facebook Messenger. Image source: Facebook

Capitalizing on Facebook's successful split of Facebook and Messenger, the company has been making early moves aimed at turning the newer messaging app into a business in its own right.

4. Apple Music shouldn't be underestimated
In October, Apple CEO Tim Cook said Apple Music boasts 6.5 million paying subscribers. While this isn't up to par with Spotify's 20 million paying subscribers (as of June), Apple's new music service has a notable audience when including all visitors to the Music app. Indeed Apple Music, with its estimated 54.6 million average unique visitors each month, and coming in 10th on the list, has the biggest audience of any music app, according to Nielsen's data.

Together, these observations highlight the dominance of these tech giants -- particularly Facebook and Google -- in digital app use. Of course, investors should take this data with a grain of salt. Nielsen's methods for measuring app use are not perfect. Based on a study of 30,000 mobile subscribers aged 13 and up, the sample size is large but not all encompassing.