Deep-is is a standalone JavaScript module that implements Node.js's `assert.deepEqual()` algorithm, with the key difference that it considers `NaN` equal to `NaN` and distinguishes between `+0` and `-0`. It is designed for developers who need a fast and reliable way to perform deep equality comparisons in their Node.js applications, offering performance improvements over wrapping `assert.deepEqual()` in a `try/catch` block.