It wasn't quite what I thinking as it isn't really "our game startup failed; let's sell game tools" but still it counts.
This is different from either providing a service and successfuly using your own software to do so or providing a service and developing as well tools specifically for your customers.
Slack was suggested by another poster as a company that pulled this off, though I'm not sure the communication tool was considered crucial to the game business.
While the legal and tools companies were together, I'm sure the lawyers enjoyed the shiny tools. But after the "pivot", with the lawyers seemingly going it alone with some of the former clients, it seems likely to me that Atrium (the tool) just wasn't offering enough of a value proposition to make the tool company profitable.
Venture money needs massive growth. Selling a tool to lawyers will get an amount of money per month proportionate to the number of fee-earners. And from the sounds of things, their tools weren't exactly going to be irreplaceable. Anyone got any direct insight as to if the tools themselves were compelling but the pivot failed, or if the tools didn't deliver?