Werk is a command runner and simplistic build system. It is intended to supplant Make in projects that need a simple build tool adjacent to a main build system, such as Cargo or NPM.
The motivating use case is an asset building pipeline for a video game, which must perform a series of expensive steps to produce an asset archive that can be hot-reloaded by a game engine.
Werk is both limited and very opinionated. It is not suited for all use cases, and it can only replace more advanced solutions, like CMake or scons, in a limited number of scenarios. However, it is suited to work together with such systems, and can be used to invoke them in a convenient way.
Werk tries to be really clever about when to rebuild files, and is knowledgeable about file modification times, but also things like the path to any commands invoked in a recipe, any environment variables used in the recipe, or changes in the results of glob patterns (like *.txt).