The keys MellowCAD answers: the drafting aids, editing and files, the window and the command line.
The keys MellowCAD answers, the ones an AutoCAD user already has in their fingers. A command is named as you would type it; its aliases are on the commands page.
Drafting aids
Key
What it does
Command
F1
Opens the help of the running command in a new tab, or these docs with none.
F2
Command history
F3
Object snap
F4
Selection cycling
F7
Grid
F8, Ctrl+L
Ortho mode
F9
Snap mode
F10
Polar tracking
F11
Object snap tracking
Editing and files
Key
What it does
Command
Ctrl+Z
Undo the last action
U
Ctrl+Y, Ctrl+Shift+Z
Multiple redo
MREDO
Ctrl+C
Copy
COPYCLIP
Ctrl+Shift+C
Copy with base point
COPYBASE
Ctrl+X
Cut
CUTCLIP
Ctrl+V
Paste the clipboard into the drawing
PASTECLIP
Ctrl+A
Select every object
Ctrl+S
Save the drawing to a file
QSAVE
Ctrl+Shift+S
Save the drawing to a file under a new name
SAVEAS
Ctrl+O
Open a drawing file
OPEN
Window
Key
What it does
Command
Ctrl+1
Show the properties of the selected objects
PROPERTIES / PROPERTIESCLOSE
Ctrl+0
Clear toolbars and palettes from the screen
CLEANSCREENON / CLEANSCREENOFF
Ctrl+9
Command line
Command line
Key
What it does
Command
Enter, Space
Runs what is typed. With nothing typed it takes the prompt's default or ends the command, and with no command running it repeats the last one.
Esc
Cancels the running command; a first Esc clears what is half typed.
↑, ↓
With no command running, brings back the commands typed before.
Tab
Completes the command name being typed; at a point prompt, steps through the object snaps under the cursor.
Shift+Space
Steps through the overlapping objects under the cursor while selection cycling shows its badge.