2.1 does not introduce new features with respect to 1.99.21, the software has been gradually refined with new features and bug fixes along the whole 1.99.x series of releases I think (I am following it starting from about 1.99.9).
Important features of 2.1 are a much improved LaTeX export filter, improved HTML export, a comment facility (for collaboration), improvements on plugin support for several programming languages (I did not test these extensively), a very nice mechanism for making it easier to use the label/ref mechanism (includes a tiptool for immediately seeing the referenced object).
2.1 does not introduce new features with respect to 1.99.21, the software has been gradually refined with new features and bug fixes along the whole 1.99.x series of releases I think (I am following it starting from about 1.99.9).
Important features of 2.1 are a much improved LaTeX export filter, improved HTML export, a comment facility (for collaboration), improvements on plugin support for several programming languages (I did not test these extensively), a very nice mechanism for making it easier to use the label/ref mechanism (includes a tiptool for immediately seeing the referenced object).