ModSim is described as '32 is a very simple but powerful application for simulating data from modbus slave devices. ModSim is an MDI application which allows you to define multiple blocks of data points which may then be accessed from a connected modbus master' and is an app in the development category. There are six alternatives to ModSim for Windows and Linux. The best alternative is ModScan. It's not free, so if you're looking for a free alternative, you could try QModBus or CAS Modbus Scanner. Other great apps like ModSim are Modbus Poll, Modbus Slave and QModMaster.
ModScan is for use in development or maintenance of multi-vendor systems utilizing the popular PLC communications protocol as developed by Gould Modicon. It allows the PC to operate as a MODBUS master device, polling a connected slave for data.
QModBus is a free Qt-based implementation of a ModBus master application. A graphical user interface allows easy communication with ModBus slaves over serial line interface. QModBus also includes a bus monitor for examining all traffic on the bus.
Modbus Poll is a Modbus master simulator designed primarily to help developers of Modbus slave devices or others that want to test and simulate the Modbus protocol. With the multiple document interface you can monitor several Modbus slaves and/or data areas at the same time.
Modbus Slave is for simulating up to 32 slave devices in 32 windows!. Speed up your PLC programming with this simulating tools. Start programming and test before you receive your slave device from supplier.
CAS Modbus Scanner is a utility to retrieve coils, inputs, holding registers, and input registers from a Modbus enabled device. Values retrieved from the device can be viewed in many different formats including Binary, HEX, Uint16, Int16, Uint32, Int32, and Float32.
QModMaster is a free Qt-based implementation of a ModBus master application. A graphical user interface allows easy communication with ModBus RTU and TCP slaves. QModMaster also includes a bus monitor for examining all traffic on the bus.