What are some alternatives?
When comparing grepWin and RegExr, you can also consider the following products
AstroGrep - AstroGrep is A Microsoft Windows GUI File Searching (grep) utility.
Expresso - The award-winning Expresso editor is equally suitable as a teaching tool for the beginning user of regular expressions or as a full-featured development environment for the experienced programmer with an extensive knowledge of regular expressions.
grep - grep is a command-line utility for searching plain-text data sets for lines matching a regular...
PowerGREP - Quickly search through large numbers of files on your PC or network using powerful text patterns to find exactly the information you want. Search and replace with plain text or regular expressions to maintain web sites, source code, reports, ...
Regulex - Open-source, regular expression parser and visualizer.