Coleman is a couple different things. It's a simple, fast, and small web server. It's also a servlet engine in C instead of Java.
The servlet architecture is a great idea, a nice simple plug-in interface for web servers, but it has some problems. First, it's tied to Java. If you don't like that language then you are stuck. Second, the performance of servlet-based web servers is inherently mediocre because they handle concurrency with threads.
Coleman fixes both of these problems; the first, by using plain old C as the API language; the second, with a new hybrid concurrency model.
See the manual pages for more details:
If you are currently using thttpd and/or mini_httpd and want to know how coleman compares, here's a little table:
|config file||ad hoc||ad hoc||JSON|
|non-local referrer blocking||yes||yes||yes|
|gzipped tarchive size||130KB||40KB||90KB|
Are you using coleman? There's a mailing list. Join the conversation!