There are a lot of build tools for Java. More than I have seen for any other language I've used. When working with Java, I've used Ant, Maven 1, and Maven 2. I know of at least a few more, and I recently found this post with a link to a poll on what build tools people are using this year (for Java).
If you navigate to the 'What Build Tool are you using in 2009?' poll (I can't post a direct link, sorry, but there are only 3 polls to choose from), you will see quite a selection of tools.
Unfortunately, right now I'm that single Maven 1.x user (along with some Ant). It's tough - things work well enough, but there is no direct path to Maven 2.x for us (oh maven.xml, you looked so helpful, but you've trapped us!). In its defense, this project was using Maven 1 back in 2004. It's not surprising that in 5 years some cruft has accumulated.
I am fed up with having to write build scripts in XML, so even if a Maven 2 migration path was simple, I'm not sure it's desired. Gant would get rid of the XML while keeping familiar territory - but I feel like I need something richer than basic Ant. Gradle looks very promising, and I've been meaning to read up on some of the threads on where Gant and Gradle are going to get a better idea of things, but I haven't yet.
Lo and Behold, while pulling up links for this blog post... I stumbled upon a post about Maven 3.
Support for several build script file formats? YAML, Groovy? Hell yeah! I am going to have to do my research on this one.
I wasn't quite sure where I was going with this post, but I think I'll sample some of the build tools I've mentioned (including early maven 3 builds) and report in on them. If I'm motivated, maybe I will do a 'Hello World' project in each build tool. Gant, Gradle, and Maven 3.