Before the Web was in evidence in 1991 (see history), there was Usenet News, which started in 1979. It grew to consist of myriad newsgroups, even in the 1980s. Computer servers, as a public service, dedicated some of their storage to a rolling database of hundreds and later thousands of newsgroups containing messages going back several days to several weeks before the oldest messages were sloughed off in favor of the latest messages. The mechanism used was a form of uucp (Unix to Unix Copy) which stored and forwarded the message base from one Computer system to another.
Within Usenet, there existed binary newsgroups that allowed freeware, shareware, updates to existing applications that were regularly made available. See a short history of Usenet.
A while back, I was reading the newsgroup: rec.puzzles, a very large online discussion group, I searched for the subset of articles that involved Sudoku (using the Unison Newsreader on Mac OSX 10.3.9). From these (over a thousand messages), There was a message relating to the Multi-Operating System product (Freeware) called Sudoku Susser by Robert Woodhead.
I’m impressed with Sudoku Susser. It is interesting because of its user interface support for various intermediate and advanced solving techniques. You can also drag and drop puzzles to solve from the Web or as files and the software will attempt to read it in.
Since the author of the books is the author of the software, Supplying the ISBN number to either book will automatically load all the puzzles in that book! The type of freeware requested is called tipware. I.e., pay what you can, if you want. I like this software’s user interface even better than that of the Seattle Times Sudoku Puzzle (which they offer via content.uclick.com), which is my favorite online web interface.
I solved the initial easy puzzle to test how the default interface worked. Every move you make is tracked. All possibilities (variable sized depending on how many) are specified in the non-starting number squares, making the puzzle a fast pleasure to solve. When highlighting a square, the non-possibilities are also shown to verify your candidate value. There are options for toggling “annoying” sound effects and an “embarrassing” timer.