[sourcesmith]

http://www.regexplanet.com/ handles regex dialects for a dozen languages and allows them to be shared.

[jhauberg]

I usually need either Python or PCRE, and for that I prefer https://regex101.com

[c0wb0yc0d3r]

Wow! I need to remember to give this a try. I usually use https://regexr.com/. I like it because it usually works for all languages and it's served over https. That is always nice!

Edit: For what it is worth, you link serves over https, too. Just not by default.