What can you do with it:
1. String together Unix-like text processing functions into a text processing pipeline.
2. Share said pipeline with friends and co-workers through a transparent link.
3. Since the functions are encoded in the URL, you can even compose functions without getting on the website! Just start typing a link: www.textpiper.com/grep?total/col?2&3/sort?asc/replace?dollars=yens
4. Your data is safe since it doesn't get out of the browser, but I'm aware that composed URLs could get logged. In future I'll add opaque URL.
It's very much a prototype and a work in progress, and as you can tell already, my UX skills leave a lot to be desired. Feedback is very much appreciated!