Two years ago I learnt new language (Scala) and wanted to find real problems to work on. So I built DocsApp[1] as real-world project as well as trying build profitable SaaS.
Few months ago I plan to sell off DocsApp, but I got low ball offer because low revenue. Then I decided to refocus DocsApp and continue to build it.
I wouldn't say DocsApp very successful, but it is getting successful now.