There are plenty of free books available as plain text over at Project Gutenberg and here
Adjust the slider to determine what percentage of each text source is used to create the mashup
Jumble Ratio (A:B) is 50:50
Source A:
-- select a source text from the dropdown menu, or paste in some text of your own --
Source B:
-- select a source text from the dropdown menu, or paste in some text of your own --