Bell percentile app

Mmmm... Game design maths. Probabilities and chi and all that jazz. I have to say I hate discussing it- it sucks the fun feeling out of the game development process, but its something you have to face.
I picked up a dungeon magazine at a boot sale a few days ago and it actually had a program in BASIC you could type in to your 8bit computers to work out if your favorite dnd dice is biased. Yep, seriously.
Personally I like to grab a handful of d10 that are identical and pick ones out at random, but other players swear by various practices such as keeping their dice only in their lucky velvet bag or rolling left handed with their eyes shut etc.
Works for me.
My friend John B says he is the worst dice roller in rpg history, and he appears to be right by the games we play. The other players started edging their dice away from him like he was a vegas cooler. He rolled a natural 20 in dnd once and had to use all his strength of will not to jump up and run around the room trampling all the prepainted plastics.

Anyway, percentile dice, like d20's have a probability issue. They are linear. Rolls have just the same chance of rolling 1 as rolling 100 or rolling 50.
Ideally (velvet and lucky left hand modifier excluded of course), when measuring a characters performance you want a bell curve. That is, your most likely to get a middling result and least likely to score an extreme.

One thing I have been thinking of doing for a while for my homebrew games is a percentile dice app that Dundred that generates bell curve results for percentile dice.

If you roll 3D100 and divide the result by 3, you get a bell curve, but of course, you would not want to do that in your head for fun (if you do, go seek help) but as an app its great to have as an option.

Another way to skew d100 is to have the player roll 2d10 and pick which one is the tens unit based on if it is a high result or a low result.
If you do this, players score hits more often, but it does not effect double digit rolls. It does make 10 no better than 9, so you get a slight blip in progression- much like shadowruns exploding dice on a six ultimately mean its as easy to cast a seventh level spell as a sixth but hey, no biggie for a maths free dice bias.
Its actually quite similar to dndnext's proposed 2d20 advantage system in some ways. If you have the advantage, you pick lowest digit d10 to represent your tens, if disadvantaged, you pick the highest.
Until I build a model on the pc and test that it could live as an optional rule. Currently advantages give you higher odds of hitting by adding to the target number.

However, the doubles as critical successes achieves a performance result of 10% strong, 88% average and 2 % as close shave (exact roll and roll of 100). So whilst not being a bell curve in terms of odds, the quality of the roll will be average most of the time.