The three most common licensed apps are

Modscan as a Client/Master, Modsim as Server/slave  www.win-tech.com

Simply Modbus (simplymodbus.ca) has separate apps for RTU master, RTU slave, Ethernet master, Ethernet Slave.

Modbus Poll (master/client)  https://www.modbustools.com/

There are a number of freeware programs as well that you can find with Google.

Don't skimp on the USB/RS-485 adapter.   At least once a week on various fora the solution is to replace the cheap USB/RS-485 adapter will a quality one (FTDI chipset).