I have thought about this a lot over the years and tried to spot these companies - many of them are the type of business that Berkshire Hathaway would love to find. Some of them are a little more visible simply because they’ve scaled and developed a moat - logistics, particularly trucking in the UK, and international cargo shipping, stand out here for me. But also social care, floristry and grocery wholesaling, weird…
I worked at a small bike shop in the 90s and when we had issues with our point of sales system we would call a number on the till and it connected us to the single developer who maintained all the software for it!