is a helpful software tool for calculating decay amplitudes in various formalisms (e.g. covariant tensor, helicity or canonical formalism).
The package has been written by Mike Williams which can be used to numerically calculate quantum field theory expressions.
Classes are provided that perform matrix and tensor operations. These are used as building blocks for field theory classes which
handle spinors, polarization vectors/tensors, Dirac matricies, etc. There are also utility methods for (analytically) calculating
Clebsh-Gordon coefficients, Wigner D functions, Regge propagators, etc.
you'll find the wiki qft++
web page. A publication can also be found on arXiv (arXiv:0805.2956) at http://xxx.lanl.gov/abs/0805.2956