UPX (Ultimate Packer for eXecutables) is a portable command-line utility for decompression/compression of executable files and can be used for multiple executable formats.
You have access to significant compression ratios that will permit distribution size reductions that rival similar tools and quick decompression times. There is no noticeable memory overhead due to UPXs in-place decompression. It allows you to list, test, and unpack your executables. Additionally, you are given checksums for both the compressed and uncompressed files; this is maintained internally.
UPX is fully extendable, allowing the addition of new executable formats or new compression due to the class layout.
If you are uncomfortable operating through the command line, don't fear; there is Free UPX which offers GUI.
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