I'm not the developer of either product, but it seems like Alive has Roslyn based which offers direct access to every step of the compiler. Right now it doesn't

I'm not the developer of either product, but it seems like Alive has Roslyn based which offers direct access to every step of the compiler. Right now it doesn't look like much difference (in fact I bet NCrunch is more stable and has better integration with NUnit and the rest of the ecosystem), but I bet (purely speculating) that Alive intends on expanding their feature set into something more extensive. Performance wise, assuming the Alive developers use Roslyn efficiently (which admittedly is difficult), they could offer a lot more semantic/syntax analysis at a way faster rate (i.e., think about solutions with 10s of projects and hundreds/thousands of classes, while having a dynamic dependency graph available-- unit tests, invariants, and even property-based QuickCheck-esque testing could easily at type-time [as in after the keydown event] or a few hundred ms after). These are all capabilities inherent of being Roslyn based though, nothing too special about Alive, just a benefit it has over NCrunch should they choose to go down that road.