Programs for Reading Text Files?

dotpl asks: "Recently I acquired a number of books in text format from Project Gutenberg and archived them for later reading. When I came to read, I realised how hard it is to read text files on the computer screen, so I thought about developing a 'reader' that you can read text files with, selecting the fonts and colors you like, and which has a bookmarking feature - a la Vim - so you know where you were reading before. Then I realised that a software of the sort must already exist. How do you read big text files without suffering from severe eye strain?" While a browser may go a long way to providing the necessary functionality, most browsers bookmarking facilities are sorely lacking for this type of work, since they don't mark the position in the page, just the page, itself. Has anything like this been written?