Boa is a single-tasking HTTP server. That means that unlike traditional web servers, it does not fork for each incoming connection, nor does it fork many copies of itself to handle multiple connections. It internally multiplexes all of the ongoing HTTP connections, and forks only for CGI programs (which must be separate processes.) Preliminary tests show boa is about twice as fast as Apache, and is capable of handling 50 hits per second on a 66 MHz '486.
The primary design goals of Boa are speed and security. Security, in the sense of "can't be subverted by a malicious user", not "fine grained access control and encrypted communications". Boa is not intended as a feature-packed server; if you want one of those, check out WN from John Franks. Modifications to Boa that improve its speed, security, robustness, and portability, are eagerly sought. Other features may be added if they can be achieved without hurting the primary goals.
Boa was created by Paul Phillips <psp@well.com>. It is now being maintained and enhanced by Larry Doolittle <ldoolitt@jlab.org>. Other possible contact people are Charles F. Randall (lost), and Jon Nelson <nels0988@tc.umn.edu>. Linux is the development platform at the moment, other OS's are known to work. If you'd like to contribute to this effort, contact Larry or Jon via e-mail.