Scramble can convert between SAM, BAM and CRAM file formats. It is a part of the Staden io_lib package.
In this regard it shares a similar goal to the Samtools view sub-command, but historically was more performant. (There is no longer any considerable difference between the two.) Now Scramble is still supported, but is also a test bed for more experimental CRAM features, such as the CRAM 4.0 version.
A few related tools in io_lib are scram_flagstat, scram_merge, scram_pileup and cram_index.