What are some of the most unique marketing strategies that you've seen a startup use?

I recently heard about a really unique tactic used by a startup to gain new customers. They were promoting a line of eco-friendly cleaning products and decided to take a guerilla marketing approach by placing their products in a public place with a sign that read "Take One Free". It was really interesting to hear how this approach not only led to curious onlookers trying out the products but also generated a buzz on social media, helping them gain new customers and followers. I'd like to hear of things that you've seen in the tech space like this!