Hello,
I've started building a small library which implements automatic simplification of C# expressions:
I guess this is mostly off-topic, so sorry about that. I wanted to mention the library here because GiNaC has been hugely influential (as has SymbolicC++).
It's a very limited library, but I think it might be useful for someone wanting to experiment with building GiNaC type functionality in C# without starting from scratch.
Ed