Alex Griekspoor sent me Harp (GitHub: sintaxi / harp, License: MIT, npm: harp) by Brock Whitten, a static web server with a focus on client-side scripting. It's built on connect, but shifts the responsibility of building client-side projects to the server:
I wanted a lightweight web server that was powerful enough for me to abandon web frameworks for dead simple front-end publishing.
It'll run as a command-line tool or Node module, so you can fit it into existing projects and use it for local development.
If you look at the source it's mostly based around middleware. A major chunk of this is terraform, a preprocessor that handles partials, layouts, metadata, and caching. Terraform is available through npm, so you could use it from outside of Harp.
I've worked with single page web apps that are entirely server independent, or traditional client/server applications. This approach mixes both of these paradigms, and seems to be generating a lot of interest. I found a recent Hacker News thread about it, and an introductory blog post that explains the development history so far.