Release 2.1 of GeoAPI contains the interfaces developed by the GeoAPI project but never formalized in any standards document.
The changes since GeoAPI 2.0 are collected in several PDF documents:
This release comes in two flavours: geoapi-nogenerics-*.jar requires a Java environment J2SE 1.4 or higher while geoapi-*.jar requires a Java environment Java 5 or higher, where the asterisk is a wildcard.
Note: GeoAPI 2.1 is a legacy release. The latest release is GeoAPI 3.0.