Mustapha Muhammad Garba
Assuming you are looking for a REPL environment for writing and testing RegEx, I will recommend the two options I consider the best for my professional use.
I only came to really master the fundamentals of RegEx only after purchasing a license for Regex Buddy which runs only on Windows OS. I still use it for most of my complex patterns. It might be old, it's still quite powerful and worth the $40 bucks I paid.
Don't let the name fool you. It's not a website to teach you the basics. It's an online editor that breaks things down for you in real time and is the closest alternative to Regex Buddy, although not quite as good. 😉