Enblend and Enfuse are console based tools to merge images into seamless panorama (Enblend) and merge bracketed images into a naturally looking low dynamic range image bypassing the HDR image creation stage (Enfuse). They are mostly used from within Hugin.
Hugin is basically a very advanced GUI for Panorama Tools, Enblend, Enfuse and a couple of other tools. It supports automatic placing of control points using autopano-sift-C and stitching to LDR and HDR (OpenEXR) using any of ca. 20 output projections. You can also use hardware accelerated preview of the output to warp or crop the panorama.
Panini is a free/libre visual tool for creating perspective views from panoramic and wide angle photographs. The name is a reference to Giovanni Paolo Pannini, a veduta artist of 18 century whose unique wide angle projection technique was "reverse engineered" by Thomas Sharpless, the Panini's principal developer, and Bruno Postle, Hugin's co-developer.