IEC 61131 is the first world-wide standard for the programming languages used in PLCs.
OATs currently supports 6 programming languages.
Instruction List, Structured Text and Quick Function Block are textual languages while Ladder Diagram, Function Block Diagram and Sequential Function Chart are graphical programming languages.
Sequential Function Chart is not a language but a common element within the IEC 61131 -3. The SFC usually needs another programming language for it's content. In OATs you can use ladder diagram and function block diagram for the graphical SFC.
OATs additionally supports the textual form of the SFC with instruction list or structured text. This programming method is also part of IEC 61131 -3.
Depending on the platform function blocks and functions can be programmed in C/C++.