Download archive into a folder. Then unpack the tarball:

tar xzf modpoll.tgz

The tarball contains multiple binaries for different CPU architectures. Add the version matching your system architecture to the path. Example for ARM platforms like Raspberry Pi:

export PATH=$PWD/modpoll/linux_arm-eabihf:$PATH

Then run modpoll:

modpoll -h

Source: Free Modbus Master Simulator and Test Tool