This simple application does what it claims - resizes images.
On the PLUS side it is simple, fast, handles RAW image files, produces a reasonable quality JPEG file and it is free.
On the MINUS side it quits after each batch conversion (even if there is only one file being converted) and it does not seem to recognise that some files are in "portrait" orientation - it produces only "landscape" orientation images.
As an alternative (but not free) I suggest SIZEROX.