All the shortcuts listed here that include CMD for MacOS can be done using CTRL on Windows.
General:
CMD + R = browser reload!!! Be careful, you will lose your work if is not saved!
CMD + W = close window!!! Be careful, you will lose your work if is not saved!
CMD + S = save, either the world (if selected) or the code (when editing)
CMD + A = select all (text only)
CMD + C = copy (text only)
CMD + V = paste (text only)
CMD + X = cut (text only)
CMD + K = open workspace (empty editor window)
CMD + O = open ObjectEditor
CMD + P = open PartsBin
CMD + B = open system browser (internal system editor for modules, classes, etc.)
Code execution: (most of them work with the current line or the code that is selected)
CMD + D = do it (executes the statement)
CMD + E = exchange (exchange the last two selections)
CMD + SHIFT + I = inspect (inspects the statement, therefore opens a window with attributes)
CMD + P = print it (prints the result of the statement)
CMD + SHIFT + P = protocol (opens a menu with all the methods that the statement/object has)
CMD + F = find (finds the selected text in the text and asks for a search string)
CMD + G = find again/next
CMD + M = do more (do the last replacement again for the next occurrence)
CMD + SHIFT + M = do much more (do the last replacement again until the end of the text)
CMD + SHIFT + F = find source/browse implementors (finds the statement in the source code)
CMD + SHIFT + B = browse class (finds the statement in the source code)
CMD + ] = indent selection
CMD + [ = outdent selection
CMD + / = comment/uncomment selection
Morph manipulation:
CMD + click / right-click only = get halo
CMD + SHIFT + click / left-click only = add object to group selection
SHIFT + drag = copy morph
= (in the world) select several objects at once
right-click = world menu (when clicked on background or context menu for e.g. button)
ALT (when dragging/resizing) = gridding (default: every 10 pixel)
SHIFT (when resizing) = keep aspect ratio
SHIFT (when transforming) = scaling
Text manipulation:
CMD + B = bold (works on selected text)
CMD + I = italic (works on selected text)
CMD + U = underline (works on selected text)
CMD + L = open font editor (works on selected text or text morph)
CMD + K = add link (works on selected text)
CMD + O = add do it/JavaScript code (works on selected text)
CMD + SHIFT + U = un-emphasize (removes all style from selected text)
CMD + SHIFT + S = convert tabs to spaces
CMD + 1 = align left (works on text morph)
CMD + 2 = align right (works on text morph)
CMD + 3 = align center (works on text morph)
CMD + 5 = set font size to 8 (works on text morph)
CMD + 6 = set font size to 12 (works on text morph)
CMD + 7 = set font size to 18 (works on text morph)
CMD + 8 = set font size to 30 (works on text morph)
CMD + + = increase font size (works on selected text or text morph)
CMD + - = decrease font size (works on selected text or text morph)
About More and Exchange
These are two operations not seen in most other environments (other than Squeak ;-), but you'll like them if you try them. More is like search-and-replace except that you don't have to plan ahead. Overtype a variable name and then, when you remember it is used elsewhere, just type cmd-M -- it will find the next occurrence and make the same replacement. You can also use cmd-SHIFT-M to make the same substitution throughout the remaining text.
Exchange is also unusual in that it depends not only on the current selection, but also the previous selection. This is a minor no-no in UI design, but you will find it to be entirely natural. For instance, select one line of text (twice-click at left margin) and then select another line, after which cmd-E will exchange those two lines. Similarly the then and else clauses of an if statement can be exchanged with this one command.