Textslave is described as 'Web based page that performs basic operations on blocks of text' and is an website in the Development category. There are more than 10 alternatives to Textslave, not only websites but also apps for a variety of platforms, including Windows, Google Chrome, Firefox and Linux. The best alternative is NimbleText, which is free. Other great sites and apps similar to Textslave are TextPipe (Paid), Text Mechanic (Freemium), WordCounter.net (Free) and Word Count Tools (Free).
One tool - One point of maintenance. With TextPipe you specify all your text processing functions in one place, rather than remembering and managing multiple manual jobs across various text editors, command line tools, custom scripts and Word and Excel macros.
This word counter & character counter tool is the web version of the popular Firefox add-on and Chrome extension that provide an extensive report about the number of words, characters, sentences... Everything is done instantaneously at the client side only.