Letgo
In the process, Letgo has become the startup world's newest unicorn - worth over $1 billion, having raised more than $375 million to date.
Letgo was founded in 2015 and is available for iPhone and Android devices. The premise is simple: Snap a photo of something you'd like to sell, post it to the app, and chat with potential buyers.
Letgo is consistently one of the top 50 free apps in the App Store, vying for dominance with a similar app, OfferUp. But Letgo is rapidly gaining ground: The company announced on Wednesday that it's hit 75 million downloads, about 2.5 times more than it had in 2016.
Here's what it's like to use the Letgo app: