nvi is a version of the vi editor which supports all the historic ex/vi features except for open mode and the lisp edit option (e.g., it has a fully implemented underlying ex mode). It contains a number of additional features, including an experimental GTK frontend in the development version.
isl is a library for manipulating sets and relations of integer points bounded by linear constraints. Supported operations on sets include intersection, union, set difference, emptiness check, convex hull, (integer) affine hull, integer projection, and computing the lexicographic minimum using parametric integer programming. It also includes an ILP solver based on generalized basis reduction and operations geared towards polyhedral compilation such as dependence analysis, scheduling, and AST generation.