Norton Commander, DOS Navigator, Windows Commander (but Christian Ghisler was forced by "you-know-who" to change the name ... now it's Total Commander, but still just as good), Midnight Commander (by far the best name) ... and there are others (anyone remember the excellent PC Tools? ... even DOSshell?). They're all variations on that theme, and all good!
I guess I should also make honourable mention of XTree Gold! And (last but by no means least, The Volkov Commander ... written by a guy called Vsevolod Volkov in Urkraine ... check it out
Just remembered "Back & Forth Professional" ... another classic that I've used a lot. It was a task-switcher that was so fast it seemed like multi-tasking (well, almost ... but this was well before OLE and stuff like that). And remember SideKick? A brilliant hack! Better stop there ... there's just too much of good old stuff like that, from what I would call the Golden Years of computing.