Include Feature Class name In Merge Toolbox

Idea created by exta on Nov 4, 2013
    I'd like to have a checkbox option in the "Merge Toolbox" to include a field in the merged feature class that would contain the name the original feature class the data came from.
    I get a lot of datasets from the field that have similar schemas. It's not hard to merge them. But I would like to know which file any given feature came from.
    Currently I have to add a field to the origial feature classes individually and calculate that field to the name of the feature class by hand and then do the  merge. With 10-15 feature classes this is a major time suck.

    This functionality was offered by Xtools in ArcView 3.3. It miss it so.