Easy.PDI (nuget): This library contains the core set of useful Personal Data Interchange (PDI) and date utility classes for .NET applications.  They can be used for calculating holiday dates, recurrences, etc.  See the project website for the code, a help file, and demos. This version contains an additional param to  Recurrence, to avoid holes in periods when an invalid date is found.
Keywords: PDI|personal|data|interchange|holiday|calculation|date|recurrence|RFC|2445