Create a single, general-purpose tool which is simple to understand but can be applied to many problems. It's like the product version of occam's razor.
The value of a product is the number of problems it can solve divided by the amount of complexity the user needs to keep in their head to use it. Consider an iPhone vs a standard TV remove: an iPhone touchscreen can be used for countless different functions, but there's very little to remember about how it works (tap, drag, swipe, pinch). With a TV remove you have to remember what every button does; the more things you can use the remote for, the more buttons it has. We want to create iPhones, not TV remotes.
Composability. Simple tools which do one thing well and can be composed with other tools to create a nearly infinite number of results. For example, the unix methodology (stdin/stdout and pipes), see The Art of Unix Programming. Heroku examples include the add-ons API, logging/logplex, and procfile/the process model.
Small is beautiful. This isn't just tools, it's also teams. Several small, autonomous, focused teams working in concert almost always beat a single monolithic team.