One of the bigger drags of Web applications development is that building a system of even modest complexity is a lot like herding cats - you need a database, an applications server, an XML engine, etc., etc. And as they all come from different vendors you are faced with solving the constellation of integration issues that inevitably arise.
If you are lucky, your integration results in a smoothly functioning system. If not, you have a lot of spare parts flying in loose formation with the risk of a crash and burn at any moment.
An alternative is to look for all of these features and services in a single package but you'll find few choices in this arena. One that is available and looks very promising is OpenLink's Virtuoso (see links below).
Virtuoso is described as a cross platform (runs on Windows, all Unix flavors, Linux, and Mac OS X) universal server that provides databases, XML services, a Web application server and supporting services all in a single package.
OpenLink's list of supported standards is impressive and includes .Net, Mono, J2EE, XML Web Services (Simple Object Application Protocol, Web Services Description Language, WS-Security, Universal Description, Discovery and Integration), XML, XPath, XQuery, XSL-T, WebDav, HTTP, SMTP, LDAP, POP3, SQL-92, ODBC, JDBC and OLE-DB.
Virtuoso provides an HTTP-compliant Web Server; native XML document creation, storage and management; a Web services platform for creation, hosting and consumption of Web services; content replication and synchronization services; free text index server, mail delivery and storage and an NNTP server.
Another interesting feature is that with Virtuoso you can create Web services from existing SQL Stored Procedures, Java classes, C++ classes, and 'C' functions as well as create dynamic XML documents from ODBC and JDBC data sources.
This is an enormous product and implies a serious commitment on the part of adopters due to its scope and range of services. Surprisingly given the scale of the product its price seems very reasonable starting at $5,000.