This is EnhancedStackSplit updated for 8.1.

Originally written by kunda.

Description:

1-Click mode

* 'mode' Button (toggle: '1-Click mode' / 'Original WoW mode'[DEFAULT])
* Split a stack with just one click when you click on one of the numbered buttons (OK(1),2,3,4,5,6,7,8,9,10 and 20). Split is placed on the cursor, so you can place it in a slot, trade, buy, destroy or what ever.

Auto Split mode

* 'auto' Button
* Automatically splits a stack and place the splitted item(s) in a free bag slot when you click on one of the numbered buttons (1,2,3,4,5,6,7,8,9,10 and 20). Free bag slots depends on ItemFamily from item you wanna split and on ItemFamily from bag(s) with free slots. Items are placed from top left to bottom right slot in a bag.

example:
Free bagslots = 20
Item with StackSize = 137

you click on 5

you get: 20 items with 5 Itemstacksize in your bag(s)
leftover = 37
(20 because free bagslots = 20)

you click on 10

you get: 13 items with 10 Itemstacksize in your bag(s)
leftover = 7

leftover and last n-stacksize remains in the original bagslot

* Note:

Auto-splitted items are only placed in the five normal bags including special bags (or less if you have not five bags).
The 'Auto Split mode' should be only accessible via bags and bank, but I did not find a good way to do this. So it's possible that this mode is available where it shouldn't be. If you try to auto split in such cases the SplitFrame can stuck. Just press ESC to close it.
Bag and Bank Addons MUST provide the bag/slot IDs in the same way the original Blizzard UI does, otherwise EnhancedStackSplit can not auto-split such stacks or you can get the stuck-error I described above.
Most bag/bank addons works perfect with EnhancedStackSplit because the addon authors made a good job

Chat Announce

To disable Chat Messages ('Chat Announce'):

Options (ESC) -> Interface -> AddOns Tab -> EnhancedStackSplit

ReEnhancedStackSplit [MN]