ugCal

ugCal is a cross-calendar date library and reference implementation designed to support date arithmetic, calendar conversions, and formatting across multiple calendar systems. The project aims to provide accurate handling of leap years, era boundaries, and locale-sensitive representations to help developers build robust time-aware applications.

Its core capabilities include support for common civil calendars such as Gregorian and Julian, as well as other systems like Hebrew, Islamic, and a configurable civil calendar. It offers conversion to and from a continuous day count (for example Julian Day Numbers or an equivalent epoch), parsing and formatting in ISO 8601 and custom formats, and time-zone aware calculations. The library emphasizes predictable behavior for edge cases and supports configurable calendar rules.

ugCal follows a modular architecture with a core date type and separate calendar backends. The core handles arithmetic, normalization, and interval calculations, while each backend implements calendar-specific rules for year lengths, leap rules, and month-day semantics. A converter component enables bidirectional date transformations, and a formatting layer provides locale-aware output.

ugCal originated as an open-source project developed by a community of contributors in the 2010s to address fragmentation in date calculations across programming languages. It was released under a permissive license and has seen multiple language bindings and extensions. The project is used in academic research, internationalization libraries, and scheduling tools requiring consistent cross-calendar behavior.