Startups that make useful niche tools available to a wider audience

My friend recently joined the Grammarly team. One really interesting comparison to Grammarly is the set of tools that help programmers write better code. Programmers have code linters that check for stylistic problems, compilers that check for invalid code, templates that help with common patterns, and more. Grammarly basically does this for the english language.

Another example of this is Dropbox, which took tools well known in the programming community like git and rsync and made them easy enough for anyone to use. 

I wonder what tools and best-practices are hidden in other fields that would be good candidates for simplification.