I am not aware of a single command that will explicitly load and execute a cassette based program but some (many?) commercial programs were written and saved in such a way that they autostarted when they were CLOADMed, perhaps it is those programs you are thinking of.
This is most likely a case of autorun program. I seem to remember autorun was achieved by saving code to be loaded in the lower memory page (first 1024 KB of Dragon's memory), overriding the EXEC vector. I also think Dragon User once published some source code to achieve a similar result.
The only other command that may autostart a program is BOOT, but that only works on a disk system (and provided the disk was created as a bootable one).