ZZIPlib provides read access on ZIP-archives. The library uses only the patent-free compression-algorithms supported by zlib. Functions are provided that transparently access files being either real files or zipped files, both with the same filepath. The zip-archive can be used in the place of a normal subdirectory. It is written in portable C.
Bork is a very small, cross-platform file encryption utility using a password-based RC4 algorithm. It is designed to be included in source code form along with the files it encrypts for long-term storage (eg on CD-R). Its minimal external dependencies are designed to make it fairly futureproof.
ArchView can open archive files online without downloading the whole archive, just like normal Web pages. It is very fast since it just fetches a small portion of the archive file from the server. It supports RAR and ZIP formats, and HTTP, FTP, and file: protocols. It can present XUL or HTML interface.