GoGrinder

Features

Loads go problems that are stored in the standard SGF format.
Allows refutations of incorrect answers to be included in the problem files.
Remembers where you were when closed and restarted.
Can save progress through problem sets to file, so you can go work on a different set of problems, and then pick up where you left off.
Filters the available problems based on tags associated with the problems, e.g. Life and Death, Tesuji, etc.
Allows the selected problems to be sorted in various orders - by difficulty, random, etc.
Keeps statistics on the number of problems that have been correctly solved in the set, and long-term stats for each collection of problems.
Allows import and export of problem sets.
Allows editing of the current problem in an external SGF editor
Splits files containing multiple problems for use with GoGrinder.
Comes with 347 problems, ranging in difficulty from 25k - 4d.
Thousands more problems are available for free on the internet - links provided in the documentation.