Rambda is a project mainly written in Ruby, it's free.
rambda - lambda calculator in Ruby Programming Language
Rubyで記述した型なしラムダ計算を行う簡約機です。
the revised alpha-rule ^^^^^^^^^^^^^^^^^^^^^^
the revised beta-rules ^^^^^^^^^^^^^^^^^^^^^^
succ ^^^^
::
&n.&f.&x.(f)((n)f)x
簡約詳細表示モードの実装