An easy-to-use streaming compression library with strong encryption.
BS Editor: Easy Compression Library is a very easy-to-use replacement of TFileStream, TMemoryStream and other TStream descendants to their analogues with compression/decompression and encryption. Compression is transparent, all the methods, properties and behavior of TFileStream and TMemoryStream are supported, so it is very simple to replace them in the application code.

Easy Compression Library does not support multi-file archives. If you need to compress multiple files to a single archive file try FlexCompress or ZipForge.

This toolkit has also ActiveX version: Easy Compression Library ActiveX.
Specification

Compiles into exe - no dll/ocx required.
Supports all the methods, properties and behavior of TFileStream and TMemoryStream.
One stream provides transparent compression/decompression for write and read operations.
Forward and backward seeks in compressed stream.
Read and write any portion of data at any file position.
OnProgress event handler.
Compression rate indicator.
Strong encryption provided by Rijndael Algorithm, the AES winner.
Could be configured to comply with U.S. and other export restrictions.
Fastest compression level is extremely fast.
Good and MaX Compression levels provide much better compression rate than Rar, Zip, etc.
Small customizable footprint (45K-100K).
Full source code available.
Includes comprehensive help and demos for Delphi, C++ Builder and Kylix. you can free download Easy Compression Library 3.60 now.