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• Valgrind
  Valgrind is a software to detect illegal memory access (and leaks) of programs.
• Random
  C++ interface to the Mersenne Twister random number generator. It also upports SIMD-oriented Fast Mersenne Twister.
• poor man's profiler
  It tells which part of a program costs more time.
• Intel Thread Building Blocks
  An easy way to parallelize a program (aka concurrent programming).

• re-try
  Test Python regular expressions interactively.

• mylib
  A library I wrote. Absolutely no warranty.

• Dictionary.com
  Random House & American Heritage. It also has thesaurus.
• Merriam-Webster
  Merriam-Webster (abridged). It also has thesaurus.
• OALD
  Oxford Advanced Learner's Dictionary.
• LDCE
  Longman Dictionary of Contemporary English.
• COCA
  The Corpus of Contemporary American English. Subscription (free) required.
• OCD
  A collocations dictionary
• Yahoo JP
  Eng-Jpn and Jpn-Eng dictionaries. Progressive & New Century. Full-text search possible.
• ALC
  The largest (and still growing) En-Jpn and Jpn-En online dictionary. Full-text search possible.
• Interglot
  Multi-lingual online dictionary (e.g. Dut-Eng). One can find multiple synonymous Dutch words for an English word.

• Cyberkidz
  Nice flash animation site (da Silva 2007).