7-Zip is a free and open-source file archiver, a program that compresses files and stores them in compressed containers called "archives." Igor Pavlov created it, and it was initially released in 1999. 7-Zip has its own archive format, 7z, but it can also read and write a variety of other formats.
FileOptimizer Portable compresses already compressed files further without changing the file format, and being totally compatible. It keeps the behavior of the file untouched, but with its size reduced thanks to several recompression and optimization techniques.