Personal thanks to fr500 for helping make this magic possible for non-keyboard systems, such as the Mini NESC/SNESC/PSC!

DOSBOX Standard:

B = LEFT CTRL
A = LEFT ALT
UP= UP
DOWN = DOWN
LEFT = LEFT
RIGHT = RIGHT
START = ENTER
SELECT = ESCAPE

DOSBOX Tyrian:

ctrl-backspace -- kill OpenTyrian
alt-enter      -- fullscreen
ctrl-f10       -- ungrab mouse
arrow keys     -- ship movement
space          -- fire weapons
enter          -- toggle rear weapon mode
ctrl/alt       -- fire left/right sidekick

MSX/MSX2:

Metal Gear 1/2: (Simply Remap whichever button you want to be the following commands!)

UP = UP
DOWN = DOWN
LEFT = LEFT
RIGHT = RIGHT
N or B button = Press the left action button, or the N key on the MSX keyboard, to make Snake punch.
It can also be used to advance the dialog.
Space or A button = Press the right action button, or the space bar on the MSX keyboard, 
to instruct Snake to fire the currently active weapon. Also press this button to utilize
an item in your inventory such as rations.
F1 = PAUSE
F4/F5 = While the game is paused press the F5 key to initiate saving the game.
To properly save the game, you must have a cassette player connected to the MSX. 
To load the game back, press the F4 key while the game is paused.

F2 = Press the F2 key to enter and exit the weapon select screen.
F3: Press the F3 key to enter and exit the inventory screen.
F4: Press the F4 key to enter and exit the transceiver screen. While on this screen, press
left or right to change the communication frequency, and press up to attempt communication 
on the current frequency.