Dave Leip's Atlas of U.S. Presidential Elections is the work of a single individual. According to the author, it was started as a paper hobby after the 1992 Presidential Election. Dave Leip uses Excel as a tool to produce the pie charts and to help build the county-level maps.
There are two distinct elements:
Important note: Dave Leip's election maps use RED for the Democratic Party and BLUE for the Republican Party. See his FAQ for more information.