A home recipe can be found at

http://patty.vox.com/library/post/homemade-limoncello-when-life-gives-you-lemons.html

It could be modified by using various citrous rinds or their mixture to a different color, taste and sweetness.  Any colorless liquor works besides vodka, e.g. white rum, gin, etc.  Limoncello is traditionally served in chilled liqueur glasses.  A sip in a hot summer evening is delightful, enjoyable and calming.  Start making it as a spring project to get ready for summer.