Early this year, Amazon CEO Jeff Bezos became frustrated that there weren’t enough applications available for Amazon’s Alexa digital assistant. So, in a meeting with the Alexa team, he urged employees to speed up certifying these apps, known as Alexa Skills, said a former Amazon employee who was in the meeting.

The number of Skills available on Amazon’s Alexa app store subsequently exploded. More than 5,000 are now available, up from around 130 in January, according to an Amazon spokeswoman. Uber, Twitter and Capital One have all built integrations so customers can use their services by talking to Alexa. (The spokeswoman declined to comment on Mr. Bezos' involvement.)