Useful online tools for StackOverflow
SQL
SQLFiddle
StackOverflow MSSQL
SQLize
SQLZoo
Regex
RegexPal (Generic)
Regexr (Generic)
Regex101 (Generic)
Rubular (Ruby)
LarsoLavtorvik (PHP)
MyRegexTester (.NET, PHP, JS, JAVA)
Programing Languages
Others