The ? and ?? are quite useful, its true, but hardly a substitute for a
real structured info tree. The problem with the GAP facilities is
that you need to know the NAME of the function or concept before you
can find it. [rest deleted]

Not so. Something like "??conjug" will give you a list of all
references involving conjugation, conjugacy, conjugate, etc. I use the
?? utility this way a lot. The reference name need not even involve
the letters "conjug", since many references have short descriptions
associated with them which involve other words and which are found by
the ?? command. Nor do you have to get the case correct, as ?? is not
case sensitive. Yes, you do have to know something about what you are
looking for, but certainly not the exact name. Yes, it is very much
like "apropos".

Yes, to use the ? you need the exact name (except case does not matter,
and actually you need only a unique initial string from the name -- the
tab-key name-completion feature will help with this if you bother to
type the cases right). You can easily get the correct name from a ??
query. Well, yes, sometimes there are several likely-looking names, so
I check them all. I find this a lot easier than following several
likely-looking branches in an info tree.