parsetree 2.0.0 was released on 2007/08/01.
I don't use parsetree myself. Since this is a major version bump, is it backwards compatible with parsetree 1.7.0? I can't really tell from the Changes, although there is no mention of such incompatibility.
Ryan Davis, one of parsetree's two developers, told me via mail, that 1.7.0 and 2.0.0 are compatible.
Thanks for looking into it. dev-ruby/parsetree-2.0.0 is now in CVS.