When one of the world's best drummers uses an app you developed to keep the tempo of his drum beat, it is no wonder that it continues to bring in the dough years after it was first released.
For Mr Zen Ho, 34, a metronome app which he developed as a side project in 2009 while holding a full-time job at the DSO National Laboratories ended up being an unexpected cash cow.
"It was just a hobby. I didn't know it would be something I would end up doing for a living," said Mr Ho, who has spent the past six years developing apps full time.
The app, Tempo, was one of the earliest apps on the Apple iTunes store back then. This was in 2009, when smartphones such as the iPhone were becoming popular and app development was still a fresh industry. The app's popularity exploded after it was featured on the iTunes store's landing page as a "New and Noteworthy" app in February 2010.
In 2014, Mr Ho discovered that drummer Mike Mangini, from legendary progressive metal band Dream Theater, was a fan of the app, even using it in his drumming tutorials on YouTube. This led to the both of them collaborating on a more professional version of the app, Tempo Advance.
Mr Ho, a computer science graduate from the National University of Singapore and a musician who plays both the keyboard and guitar, chalks his app's success up to a mixture of luck and good timing.
"It made sense to quit my day job and do more app development, since it was making me more money than my day job," he said.
Tempo's success has enabled Mr Ho to live off its royalties for the past six years, and even let him save enough to buy an apartment at an Orchard Road condominium.
While he declined to reveal how much he made from the app in total, he said it provides him with a monthly five-figure amount. "It is very good money, especially since it is largely passive (income)," he said.
This has freed him up to work from home on other projects, which the father of one - who is expecting a second child - is content with. He is married to a school teacher. During the past few years, he worked with various parties on app development, but none reached the same level of success as Tempo did.
Tempo is still going strong, selling for $4.48 at the app store, although Mr Ho said sales have declined steadily over the years.
But times are changing, he said. Generating such revenue from apps is not so easy now, which is why he is taking a break from app development after his last project a few weeks ago.
"The market has matured. Small players like myself will find it very hard. It was the gold rush last time," he said.