Expressions is described as 'minimal, distraction-free tool for experimenting with regular expressions' and is an app in the Development category. There are more than 25 alternatives to Expressions for a variety of platforms, including Windows, Online / Web-based, Linux, Mac and Self-Hosted solutions. The best alternative is RegExr, which is both free and Open Source. Other great apps like Expressions are regular expressions 101 (Free), Expresso (Free), RegexBuddy (Paid) and iHateRegex (Free, Open Source).
Easily test your regular expressions against a sample body of text in a native UWP app designed for Windows 10. Just type your regex and it instantly begins matching as you type. Any capture groups are automatically highlighted, and the app works completely offline.
What RegExpEditor is can be said easyest by telling what it is not: It is not an editor for regular expressions. Although it can be used for this purpose. Instead RegExpEditor is a text editor that allows you to alter text using regular expressions.