CrystFEL is a suite of programs for processing (and simulating) Bragg diffraction data from "serial crystallography" experiments, often (but not always) performed using an X-ray Free-Electron Laser. Compared to rotation data, some of the particular characteristics of such data which call for a specialised software suite are:

The sliced, rather than integrated, measurement of intensity data. Many, if not all reflections are partially integrated.
Many patterns (thousands) are required - high throughput is needed.
The crystal orientations in each pattern are random and uncorrelated.
Merging into lower symmetry point groups may require the resolution of indexing ambiguities.