102 billion is a heckuva lot of mobile app downloads

App stores are set for a strong 2013, according to new data from research firm Gartner.

The company on Thursday revealed that total app downloads worldwide will hit 102 billion this year, up from the 64 billion apps that were downloaded last year. Next year, that figure will jump to 139 billion apps, and reach a high of 268.7 billion by 2017.

Free apps have always proven more popular, accounting for 90 percent of all downloads last year. But their popularity will only soar in the coming years, Gartner says, with free apps accounting for 94.5 percent of all downloads in 2017.

Not surprisingly, given their popularity, Apple's App Store and Android-based application marketplaces will dominate the mobile landscape. By 2017, over 90 percent of all apps will be downloaded to an iOS or Android-based device. Still, it's not all good news.

"These app stores are still increasingly active due to richer ecosystems and large and very active developer communities," Gartner research director Brian Blau said today in a statement. "However, we expect average monthly downloads per iOS device to decline from 4.9 in 2013 to 3.9 in 2017, while average monthly downloads per Android device will decline from 6.2 in 2013 to 5.8 in 2017."

So, why the decline? According to Blau, Gartner expects users to boot up the same apps rather than try out new ones as time goes on and they find options they like.

Still, developers can expect stronger revenue this year. Total app revenue will hit $26 billion this year, up from $18 billion last year.