GNU Radius is a RADIUS server and an accompanying set of monitoring utilities. It features MySQL and PostgreSQL interfaces for authentication and/or logging (the ODBC interface allows you to use almost any existing DBMS for that purpose), the ability to rewrite RADIUS requests from various NASs to normalize them to a more understandable format, and the ability to completely customize the behavior of RADIUS authentication and accounting based on NAS and user attributes.
Serveez is a server framework which provides routines and help for implementing IP-based servers (TCP, UDP, and ICMP). It is also possible to use named pipes for all connection-oriented protocols. The package includes a number of servers that work already: an HTTP server, an IRC server, a Gnutella spider, and some others. One of the highlights is that you can run all protocols on the same port. The application itself is single-threaded, but it uses helper processes for concurrent name resolution and ident lookups.