Here's how this works:
Put the decimal numbers in the 'Decimal' box, with each separate value on individual lines.
Click the 'Convert!' button to convert each of the decimal numbers to hex.
Click the 'Change Hex to Little Endian' button to convert each of the new hex values into little endian.
Note: this currently only works for words of 2 bytes, and all decimal numbers off less than 4 digits are word-aligned with zeroes.
This was made primarily for creating Pokédex lists, where you would enter the National Pok√©dex numbers on individual lines, for example in alphabetical order, and then convert it so a FireRed ROM could read it.