Looking for some fast, simple and stable RPC library I stumbled upon MessagePack project which seems to be very good. It is also under active development.
If you used it
Well, after some time I found that MessagePack is not well-documented (there was even non-working tutorial in Wiki for Java), there are like 7 outstanding bugs several months old without any replies. Code even is not JavaDoc'ed so that you can take and learn it quickly...
But it seems developer activity there is quite high despite of some outstanding pull requests from the community, that are several months old.
So, well, if GPL suits you, go for ICE. If not... don't know yet. Still looking.
I'm also looking into a fast, cross-platform, cross-language, non-GPL-licensed RPC library.
From looking at the C++ source of MessagePack it seems that it doesn't work on Win32 though, which is a requirement for myself.
Except for that that single item it is on top of my list of serialization/RPC libraries.