Fan – the new kid in town. Fan’s USP is its portability across Java VM and .NET CLR (and I assume Mono as well). Other than this, it seems to have combined good things from multiple worlds. Not only does it inherenly support objects and closures, but it also tackles concurrency with REST oriented transactional memory. The API currently abstracts away abstracts the Java and .NET APIs, but the team takes pride in portability across other VMs too. So, if you are writing an application which might run on various virtual machines, then Fan can be your best bet.
It will be interesting to see how much of this is achieved because at times .NET and Java APIs seem to follow diverse philosophies. Also, it will be critical to see if Fan, with abstraction over the virtual machines, which already abstract the underlying functionalities, will be able to come up with the right balance of elegance, productivity, performance and completeness to appeal to the programmer.