FDRTools Basic is the gratis variant of FDRTools. The range of functionality is identical compared to the Shareware FDRTools Advanced.
However, there is a clear distinction to the Advanced variant: FDRTools Basic ist less suited for the processing of many and large images as it does not support parallelised - and hence much faster - image data processing. Furthermore FDRTools Basic is available as 32-bit version only, imposing limits on the size of processible images.
FDRTools Basic is perfect for hobbyists who occasionally want to create high quality tonemapped images for free.
If you are a first-time user trying to evaluate the possibilities of HDR imaging and Tonemapping, you should try FDRTools Advanced. You can use it for free also, the resulting images will have a watermark.
You will find further details in the description of the Advanced version.