According to the new App Annie retrospective, 2015 was a year of significant growth in app sales. Leading the way were games, online dating and music-streaming apps, while apps for wearables appear to be the next big emerging U.S. market.

The report notes that games were still by far the most revenue producing app vehicles, accounting for 75 percent of total iOS App Store revenue and a whopping 90 percent of Google Play Store income.

Other app types, however, made big gains, with subscription apps for dating and music and video streaming leading the way. Games, ridesharing/taxi and mobile-commerce apps made significant gains as well, especially in Asian markets. The story in the U.S. was a bit different, however, with significant saturation having already occurred.

"Although there is still room for new smartphone subscribers in the U.S. market, it is saturated - especially among the demographics whose members are likely to convert to paid users," the report states.

"Given this, competition among Apple and Google (and Microsoft and Android OEMs) for existing users will intensify across all fronts. From smartphones and tablets to watches and TV accessories to AR and VR and device categories yet to be released, one thing we can definitely count on is that the U.S. will remain a massive and growing opportunity for app developers."

When it came to specific apps showing growth, Tinder showed big gains in the dating sector, while in music streaming, Spotify ruled many regions in subscriptions and revenue, although Pandora still took the top spot in the U.S. Amazon was the top retail app in many countries, while Uber, the only real global player in the taxi app sector, took the top or second spot in many of the countries in which it competes.

When it comes to what the report [pdf] describes as "the next frontier" in mobile apps, fitness and wearables led the way, with the introduction of the Apple Watch having significant impact.

The report concludes that going forward, however, app developers need to take advantage of opportunities to create unique apps for wearables, which will differentiate themselves from those currently on sale for smartphone use.