Kirill

Codesys was developed in Germany and is used for programming by some German and international vendors. The environment supports IEC 61131-3 languages and has plenty of add-ons. Interface is a bit quirky, but relatively easy to start using. Modbus programming is done in a convenient way too.  Here is the list of the most known PLC brands supported by Codesys: Schneider-Electric / Modicon - the environment is called Unity Pro Beckhoff GP Systems GmbH / Regul RX00 - the environment is called Epsilon LD, free download and use is available from the website   Bosch-Rexroth Mitsubishi Omron WAGO Hitachi    

There is a new alternative on the market. First, a disclosure - I work for this company, GP Systems GmbH. The line of controllers is called Regul RX00 and combines increased requirements to the availability - yes, we designed them initially for the process industries and before had extensive integration experience of Siemens. One of such features - switchover in 5 ms. Removed limitations on how modules could be placed in the system, added fiber optic option between racks (even CPU), all the common protocols (OPC, Modbus, IEC 101/104) to integrate with other systems, and created a free programming tool with IEC 61131-3 languages.