The best replacement for ironpython is cpython.

The best alternatives to ironpython are rated as following:
★★★★★  cpython
★★★★  boo
★★★★  ironruby
★★★★  jython
★★  activepython
★★  pypy
★  f#
★  python.net

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Speaking about ironpython, one probably shouldn't forget about sharpdevelop.

Other search terms related to ironpython and their ratings are:
★★★★★ sharpdevelop
★★★★ numpy
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ironpython
cpython
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