Lift provides the best features for building interactive web applications:

Super simple and wicked powerful Ajax and Comet coding. This lets you build more interactive, user-friendly sites.
Amazingly concise code with the powerful type-safety of Scala. This means more time spent coding features and less time writing tests or chasing parameter mis-matches.
Runs on all standard JEE (Java) application servers including Jetty, Tomcat, WebLogic, etc. This means you get the performance, scalability and compatibility of the best web infrastructure around.
Built-in security means more time focusing on your application and less time being defensive about parameter tampering, SQL injection, Cross Site Scripting and other nasty attacks.

Lift is built on Scala, a hybrid Functional and O-O language that compiles code down to the Java Virtual Machine. Scala code can call any Java code and make use of all Java classes. Java code can call some Scala code. Lift applications are packaged as WAR files and can be deployed on any Servlet 2.4 engine (e.g., Tomcat 5.5.xx, Jetty 6.0, etc.)

Lift code is as clean and brief as Rails, yet performs at least 6 times faster and is multithreaded. Additionally, because Scala is strongly typed, the compiler catches type errors. For example:

 User.find(By(User.email, "foo@bar.com")) // legal
 User.find(By(User.birthday, new Date("Jan 4, 1975"))) // legal
 User.find(By(User.birthday, "foo@bar.com")) // compiler error

Welcome to the Lift Web Framework