A few like Wakemate and Octopart come to mind where they seem to serve small markets now, but it's easy to see how they could branch out into huge adjacent mark

A few like Wakemate and Octopart come to mind where they seem to serve small markets now, but it's easy to see how they could branch out into huge adjacent market space - not necessarily as obliquely as Microsoft starting from Altair Basic, more like Amazon starting out as just an online bookstore.