i'm the developer of freerouter.nop.hu which is a free, open source router written in java.
it can do a lot of fancy networking stuff, mainly focusing on telco techologies,
so except a lot of mpls and related topics from it.
since it's completely a user-space thing, it is very useful to build
big topologies to try out things before they hit prod networks.
anyway it can do a lot more since it's a fully featured router.
if you're interested in packaging it, please let me know!
thanks in adance,
ps: i've filed a bug (#783482) for it long ago but nothing happened.