As you've probably already realised, I'm a huge fan of the Gambit Scheme implementation which is highly performant and compiles into a standalone executable.
Gambit has also been proven to support tens of thousands of concurrent lightweight threads which helps make it an ideal platform for web applications. This coupled with it's rare ability to serialize continuations places it as a front runner for web applications in the 21st century.
Unfortunately there is little infrastructure there at present to support web applications ... or so I thought. It turns out that a tremendous amount of effort has gone into developing a framework called 'Black Hole' by Per Eckerdal and Mikael More. This is a continuations based framework that is built on top of a module system for Gambit. I look forward to seeing this being released in the very near future.
To support this effort, I have developed a pure Scheme MySQL interface for Gambit that is currently in the Gambit Dumping Grounds. The advantage of a pure Scheme implementation rather than a C binding is that it won't block your thousands of lightweight threads whilst your OS thread is stuck in C land.
Currently the implementation supports logging on with new and old authentication methods, switching schema's and DML and DDL using dynamic queries. I'm currently adding support for prepared statements which I would consider essential before building a persistence layer for Black Hole or anything else.
I'd love to do the same for Oracle but unfortunately Oracle don't publish the protocol for SQL*Net so this is not possible. Hopefully Gambit will devise a way to call C with an OS thread so as not to block the lightweight threads and then we can use the OCI interface.