What is the keyboard shortcut for AutoSum?
In Grid by Zaweba the AutoSum shortcut is Alt+=, as in other spreadsheets. It writes a SUM of the numbers above or beside the cell for you to check.

Alt+= is the AutoSum shortcut. In Grid by Zaweba, press Alt and the equals key in the cell below a column of numbers, or to the right of a row, and Grid writes a SUM formula covering the numbers next to it. Press Enter to accept it. It's the same shortcut as in other spreadsheets, so your habits carry over.
What AutoSum does
AutoSum looks at the cells next to the active cell, usually above it and otherwise to the left, finds the run of numbers there, and writes a SUM formula for that range. Before you press Enter, the range is highlighted, so you can see what it picked. If it's wrong, drag to select the right cells, or type the range yourself, then press Enter.
It stops at the first blank or text cell, so a column with a heading at the top sums only the numbers below the heading. A gap in the middle of the numbers will stop it short, which is the main thing to look out for.
More than just sums
AutoSum on the ribbon also offers Average, Count, Max and Min. They work the same way, picking a nearby range and writing the formula for you. Alt+= gives the sum, the one most people want; use the ribbon button's options for the others.
Summing several totals at once
Select a block of empty cells under several columns of numbers and press Alt+=. Grid adds a SUM under each column in one go. Select empty cells beside rows of figures instead and the totals go beside the rows.
Even quicker: the status bar
If you only need to see a total, not keep it, select the cells and look at the status bar at the bottom of the window. Grid shows the Average, Count and Sum of the selection there, with no formula needed. It's ideal for checking a figure on a bank statement or a receipt.
Other shortcuts worth learning
A handful of keys cover most daily work, and Grid follows the standard spreadsheet set. Ctrl and an arrow key jumps to the edge of the data. Ctrl+Home goes to the top. F2 edits the active cell, and F4 cycles the dollar signs in a reference while you're editing. Ctrl+1 opens Format Cells. Ctrl+Z and Ctrl+Y undo and redo. Ctrl+F, Ctrl+H and Ctrl+G open Find, Replace and Go To. F11 makes a chart from the selection, and F9 recalculates.
For filling, Ctrl+D fills down and Ctrl+R fills right. Ctrl+Enter puts what you've typed into every selected cell. Alt+Enter starts a new line inside a cell.
Help > Keyboard Shortcuts lists them all inside Grid, which is handy until they become second nature.
When AutoSum gives the wrong total
Numbers stored as text are the usual cause. They look like numbers but SUM skips them. They often sit on the left of the cell instead of the right. Convert them with VALUE, or re-enter them.
A filtered list is the other trap. SUM adds hidden rows too. Use SUBTOTAL or a table's total row when you want only the visible rows counted.
Alt+= is one of those shortcuts that pays for itself on the first day. In Grid by Zaweba it works exactly as you'd expect, along with the rest of the shortcuts you already know.