The thermodynamic engine used "under the hood" is Open Calphad. The plots are generated with Gnuplot (2D and 3D plots) or xtk (online interactive 3D). The "glue" that holds the thermodynamic engine and the plotting programs together is the "ocplot" command of ATAT.The data comes from a variety of sources, most notably:
First enter the elements of interest and click search (or press enter). Your are then given a choice of databases.
The TDB link points to the database file while the doi link points to the original paper. The crossref link points to the appropriate entry in CrossRef to allow you to easily download citation info in any format (click on the "actions") menu in CrossRef.
Clicking on the "View" button, after selecting one of the database, gives you a (crude) preview of the phase diagram. You can specify a lower and upper temperature of interest. If both temperature limits are the same, an isothermal cross-section is generated. The accuracy/quality of the preview is controlled by the "number of samples", which indicates how many equilibrium calculations will be used to generate the phase diagram.
By default the plot is created with Gnuplot and the corresponding script can be obtained by clicking "Download Gnuplot code" . This is useful to include in a paper or to rotate 3D plots interactively (off-line). Checking the box "Interactive 3D" invokes the Xtk viewer, which enables online interactive 3D.Binary and ternary isothermal sections are shown as a 2D plot. Ternary phase diagrams and quaternary isothermal sections are shown as 3D plots.
The plots are still rather crude (do not blame Open Calphad for this, as this is in large part due to the ploting algorithm used).
Below the plots, some log files are reported, to help in debugging.