UPX

UPX is an open-source and universal executable file compressor developed for various operating systems and executable file formats. Its primary goal is to significantly reduce the disk size of executable files without sacrificing code functionality or performance.

A file compressed with UPX is automatically decompressed in memory at runtime and continues to run smoothly like a normal program. This means you don't need to manually decompress the file to run the program.
Key Features and Advantages of UPX

    High Compression Ratio: Typically reduces the size of executable files by 50% to 70%, saving disk space and network bandwidth.

    Instant Opening: Compressed files open instantly in memory; this does not cause a noticeable slowdown in system performance or boot speed.

    Multi-Platform and Format Support: Supports many popular operating systems such as Windows (PE), Linux (ELF), macOS (Mach-O), and numerous file formats.

    Open Source and Reliable: It is a completely free and reliable tool licensed under the GNU General Public License (GPL). It uses algorithms recognized in common security software to avoid confusion with malware detection.

    Dependency-free operation: Compressed files continue to run without needing any additional DLLs or external libraries.