In the days of Windows 3.1, replacing progman was the third biggest category of windows software. The numbers of win31 shells is still legion, but way back then, was still even more.
Some proggies that offered no ShellDDE support still used progman to effect this.
Still, some shells were as big as the OS itself (eg "Snortin' Norton" NDW, or MS-Bog [msbob]). Some were even adds (wps4win), or even paradoes (Bubba, Bob's country cousin). Both NDW and MS-BOB supported apps that ran only in the shell.
While much of today is about "adding things into Windows", much of the hacking at my time was "lean and mean" stripdowns. You should understand that a 120 MB was a huge drive back in '92, so installing 15MB of DOS, 15 MB Windows and 15 MB shell, means that the assorted OS versions take something like 45 MB. One learns how to cull apps as to what is removable.
Two complete applications, which came on ten floppy diskettes, were pruned down to a single uncompressed disk. I managed to mangle five versions of civilisation (10 diskettes), into a 3-diskette install, even to the extent that different versions do not see each other's saved games!
One of my favorites was praxim. This is a command line + toolbox, one sees from these two shots.
Here is praxim with two tool boxes, and a command line.
I have just typed "toolbox /?" at the prompt. This brought up the Command Help partly visible middle left. Right shiws some of the inbuilt commands of praxim. Scandir is a kind of tree index used by praxim. One wonders why this was never standardised.