The help command in the Mongo Shell will give you this :

> help
    db.help()                    help on db methods
    db.mycoll.help()             help on collection methods
    sh.help()                    sharding helpers
    rs.help()                    replica set helpers
    help admin                   administrative help
    help connect                 connecting to a db help
    help keys                    key shortcuts
    help misc                    misc things to know
    help mr                      mapreduce

    show dbs                     show database names
    show collections             show collections in current database
    show users                   show users in current database
    show profile                 show most recent system.profile entries with time >= 1ms
    show logs                    show the accessible logger names
    show log [name]              prints out the last segment of log in memory, 'global' is default
    use <db_name>                set current database
    db.foo.find()                list objects in collection foo
    db.foo.find( { a : 1 } )     list objects in foo where a == 1
    it                           result of the last line evaluated; use to further iterate
    DBQuery.shellBatchSize = x   set default number of items to display on shell
    exit                         quit the mongo shell
 

We could map the alias 'use'='change database'

We will have to think how to map the show commands to the list command with aliases since the alias name can't have a space in it.

> We could map the alias 'use'='change database'
Issue #9145 had the following variables set to false by default:
  . CLI_SHELL_LINE_INTERPRETER_EVAL_IMPLICIT_CMD
  . CLI_SHELL_LINE_INTERPRETER_PERFORM_ALIAS_EXPANSION

Even we set defaults back to true for these variables, there still have some other problems need to be solved. As of today, none of non-object commands will work in MongoShell:
   mongo> help
   function (x) {
       if (x == "mr") {
       ...
   The output is the definition of the help(x) function.
   mongo> help connect
   missing ; before statement
   mongo> show dbs
   missing ; before statement
   mongo> use Northwind
   missing ; before statement
   mongo> it
   ReferenceError: "it" is not defined.
   mongo> exit
   ReferenceError: "exit" is not defined.
   mongo>

Even we set defaults back to true for these variables, there still have some other problems need to be solved. As of today, none of non-object commands will work in MongoShell:

Nhi is going to take a look into this once he's back from vacation (6/4)

>> Even we set defaults back to true for these variables, there still have some other problem
>> need to be solved. As of today, none of non-object commands will work in MongoShell:

Nhi doesn't need to look at this.  The Shell is working correctly.  The only problem is that the TopLevel.help() function is not implemented in MongoScope.  See issue #9213