The IPOPT distribution includes an interface for CUTEr5 (for solving problems modeled in SIF), and also a Matlab (mex) interface which allows you to use Ipopt from Matlab, see
There are also interfaces maintained by other people:
The GAMSlinks project on COIN-OR, maintained by Stefan Vigerske, includes a GAMS interface for Ipopt, see https://projects.coin-or.org/GAMSlinks.
The AIMMSlinks project on COIN-OR, maintained by Marcel Hunting, provides an interface for Ipopt within the AIMMS modeling tool, see https://projects.coin-or.org/AIMMSlinks.
Edson Cordeiro do Valle has written an interface to use Ipopt from
Another Scilab interface is available here: http://forge.scilab.org/index.php/p/sci-ipopt
An interface to the python language is available here: http://code.google.com/p/pyipopt
Andreas Waechter 2010-12-22