David MacKay has put the textbook he wrote online for everyone to download in a variety of formats. If you find it useful, consider buying a copy.
An open source utility that will crack the password used to encrypt .rar, .zip, and .7z archives. Runs multi-threaded to speed things up because it uses a brute-force attack.
Zopfli is a new data compression algorithm from researchers at Google which seems to work better than most existing compression algorithms out there. The trade off is that it can take much longer to finish compressing files, but more space and transmission time are saved. It is recommended for compress-once-distribute-many-times use cases.