I am relatively new to the world of Java and Maven, but I couldn't imagine starting a new Java project without using Maven.
The idea of providing a human-readable project model is something that I would imagine is universally desirable across many languages. This is especially true when your application relies upon numerous external libraries.
Are there any other project management or build tools for languages other than Java that are similar in nature to Maven; that is, that provide a mechanism for the project maintainer to specify dependencies and build order?
Here's some I know of. As to whether they are the most appropriate tool for a given language, form your own opinion.
Arbitrary "integrations" can be handled by using the exec-maven-plugin to invoke the relevant compiler and binding the execution to the compile phase.
There are also Maven-like products such as Byldan for .Net
Updated with Flex Mojos and dotnet-maven-plugin at Pascal's suggestion.