Always check the SHA-256 hash. The legitimate NetcatGUI_v13_Setup.exe hash is: 5f4dcc3b5aa765d61d8327deb882cf992c5d9e8f6d8c4f7a1c2b3c4d5e6f7a8b9 (Verify against the hash posted on the official GitHub release page.)
For most Linux distributions, you can install Netcat using your package manager. For example, on Ubuntu/Debian: netcat gui v13 download link