This is a module to modify the order, invoice, shipment and credit memo numbers in Magento 1.9 (NOT in Magento 2 - feel free to fork this module and update it to Magento 2!). Many variables and counter options are available in the format string.
Install via modman:
$ cd <magento root>
$ modman init # if you've never used modman before
$ modman clone ssh://open-tools.net@open-tools.net/var/www/open-tools.net/private/git/Magento_Ordernumber/
Visit System -> Configuration -> Sales -> Customize Order Numbers and set it to Yes to enable custom numbers for certain number types. All configuration is done there, there is no separate component or view available.
Note that it's disabled by default.