https://github.com/gruseom/numen
There are also very few moving parts. In arc you have access to the entire stack from http request to http response, at the raw text level. The goal is simply to generate the text as quickly as possible. And racket turned out to be a good long term bet; people underestimate how optimized it is.
Numen [1] is an Emacs REPL we wrote for Parenscript + Node.js a few years ago. The version that's up on Github works with a different Lisp called Lumen [2] that compiles to JS and Lua, which we created partly as a Parenscript successor (it's self-hosted) but mostly as an experiment in a table-oriented Lisp [3,4]. But the differences between that REPL and the Parenscript one are trivial, and I can put the PS REPL up if anyone's interested. We still have plenty of code in Parenscript—including a Chrome extension we wrote to support HN moderation—so I use it every day.
1. https://github.com/gruseom/numen
2. https://github.com/sctb/lumen