FlashDEG is a C/C++ tool for differential gene-expression analysis of bulk RNA-seq data. It reads count matrices and sample metadata, applies DESeq2-style statistical methods, and exports fold changes, p-values, and adjusted p-values. It offers a command-line engine and a desktop interface, with documented source support for Windows, Linux, and macOS. Optional analyses include likelihood-ratio testing, normalized outputs, and effect-size shrinkage.