I decided to add .NET support to my PHP (Perl-style) regex tester at http://www.myregextester.com since I wanted to occasionally test variable-length lookbehind assertions for use with .NET and of course PHP does not allow for (while it does allow for fixed-length lookbehind alternations of possibly differing length, which is more than Perl itself actually supports).

The processing of the pattern with a .NET regex engine is an optional choice at the tester as it defaults to using the PHP's Perl syntax regex functions.