OPTIMIZER contains experimental and development versions of R optimization packages, esp. unconstrained or box constrained problems and utilities for testing of functions, evaluating proposed solutions, and improved optimization interfaces.
The project summary page you can find here.
Packages for optimization and solution of nonlinear systems of equations include
Packages for utils functions include
There is an attempt to build an evolving "handbook" or "cheatsheet" for nonlinear least squares computations for R. The source file is of type .Rnw and can be processed with the knitR tools. This is nlshb.Rnw, with the latest output file uploaded as nlshb.pdf