NCL the NEXUS Class Library.
For odd (but still very boring) historical reasons, branches/v2.1 is the
primary line of development for NCL. The trunk and 2.1 are periodically synced,
so they should basically offer the same set of features. But additions tend
to occur on 2.1.
branches/v2.2 is intended to be version of 2.1 that supports
SWIG-bindings. It currently does this for python only. For non-SWIG users,
v2.2 is not appreciably better than v2.1.