Rubular: a Ruby regular expression editor and tester http://rubular.com/
Python Regex Tool http://www.pythonregex.com/
PyRegex http://www.pyregex.com/
Pythex: a Python regular expression editor https://pythex.org/
Regex Tester http://regexpal.com/
RegExr: Learn, Build, & Test RegEx http://www.regexr.com/
Online regex tester and debugger: JavaScript, Python, PHP, and PCRE http://regex101.com/