The idea for my product first came to me when a friend in university had trouble staying focused on writing papers. He was constantly playing World of Warcraft and needed a way to temporarily block himself from playing the game. So I quickly made a little VB.NET app and service that would watch for the game executable and kill the process if it starts. It did the job well enough and he ended up graduating :)
At that point, some other students approached me and asked for my little app to help them study. That's when, half-way through university (2010), I made a website for my app and had it available for free. I continued to maintain it and over 4 years, added more features including: blocking websites, adding breaks, scheduling, and passwords.
In 2014, I split the product into a free and paid tier. It wasn't an easy decision, but I was spending a lot of time on it by this point and customer support was also starting to take a serious hit on my personal time. In about two years (2016), I was making more money from the paid product than my well paying government day job. So, I decided to quit my job and work on my business full time.
Although I felt it was risky, the alternative was passing up an opportunity many people dreamed of having. I never planned to start a business in the first place and I kind of felt/still feel imposter syndrome. For now, I'm just enjoying my new found freedom and continue to be thankful for my new job. I'm going to keep it a lifestyle business for now, but I wouldn't be opposed to selling it as my exit plan.
I've spent (effectively) $0 in advertising since developing it and I'd say my customers come from organic search, external links, and word-of-mouth.