One of the most useful tools in my computer toolbox is the Microsoft Excel. The ability to make legible tables and lists is a boon to any wargamer who writes like a doctor. Of course, the Word/Powerpoint package of MSOffice work well together with it as well (Note- I'm using an earlier version of MS Office, so the newer versions look a bit different). Here are some of the uses:
1. Prototyping rules- Sometimes all I have for a rule idea is a table or two and an outline of the turn sequence. I just type them into Excel, print them out and playtest them. I take notes on the back of the page (such as changes, what works and what does not) and make the changes in Excel and repeat (playtesting for me is a process of running the game again and again ad nauseum- until I go on to another set of rules for a while for a break :D ).
2. Creating nice tables for my quick reference cards and rules- You can create nice looking tables and cut and paste them into Powerpoint (for quick reference cards) or Word (for my rules).
A word of advice though- be organized when saving the files for a ruleset. If I have a ruleset called "Micro WW2" I'll abbreviate it "DSRMW2" (Don's Stupid Rules for Micro WW2). That way the 3 files for the whole ruleset are DSRMW2.XLS (the excel tables), DSRMW2.DOC (the rules) and DSRMW2.PPT (the powerpoint quick reference charts).
3. Creating consistent points values for army lists- Some rules I create require a point basis to help determine forces. This requires a calculation of various attributes (like armor, attack, range, morale, strength, etc). For my ancient 15mm ancients Rules (DSRV), there are a lot of attributes and a lot of armies to calculate for. Instead of calculating this by hand, I created a spreadsheet that holds all the stats of the units, and used formulas to calculate the points value of that unit automatically.
First, I had to figure out how to rate units for points basis. This required multipliers that I had to play with in order to weight things well. I created a sheet that holds all the weights (for all those who don't know you can name a cell so that you don't have to reference it the formula by its long name). I colored the background yellow where the values are changeable.
Second, I created a sheet with all the army lists and all the values. Black text will be displayed, red text will be hidden (its used for calculation) and gray text is a calculation that also will be hidden. I input values in the red and black columns and the points are automatically calculated.
To create a reference sheet for the armies, I hide all the black and gray text, then cut and paste it into powerpoint.
Voila ! Now I can change the values easily and print out the final result. I can also easily add troop types and armies as needed.
Excel (and the MS Office Suite) are excellent tools for the wargamer.