MadLab
MadLab Tesuji Solver is a program for solving open-space capture problems. Written in Java, MadLab runs on all major platforms and is available at http://www.t-t.dk/madlab. MadLab was commercial but is now free of charge in its full version.
The program guarantees 100% correctness of its solutions, and it can also analyze whole games, scanning them for tesuji's.
MadLab comes with 997 capture problems extracted from real high-level games. The 997 capture problems can also be freely downloaded as sgf files here: http://t-t.dk/madlab/problems.
Example of an open-space capture problem (LuckySProblem):
The problem is open-space since the marked stones are not surrounded by outer walls of stones like semeai or tsumego problems. MadLab is aimed at open-space capture problems, and the engine is based upon the so-called Lambda Search algorithm.
Author of MadLab: Thomas Thomsen.
SiouxDenim - (13 Apr 2010) the links on this page no longer work. It is not obvious if MadLab still exists.
Wayback to the rescue: http://web.archive.org/web/20080915132417/http://t-t.dk/madlab/problems/index.html
SiouxDenim - the 997 problems are available as a .zip file, but it is not possible to download MadLab itself.
Thomas Thomsen (30. Dec. 2011) - Sorry, MadLab got temporarily unavailable when I changed web server host. This is now corrected, and in addition I decided to make the full MadLab version available for free. I am (too) busy with other software development at the moment, so feel free to try out MadLab. The 997 problems are probably also funnier to play around with in MadLab, since MadLab will patiently refute any defensive move you might come up with.