iGTD version 1, even the retooled Leopard updates, seems to have problems under OSX 10.5.8, saving to its database and syncing with iCal. The last update was a year and a half ago. iGTD version 2 runs, but bears no resemblance to the elegant simplicity of version 1 and cannot import data from earlier versions, requiring one to re-type everything. Version 2 is in perennial (but polished) alpha, last update same time frame of about 18-19 months ago. I wouldn’t count on it – looks to be a dead end, and it’s a real shame. If anybody knows otherwise, please add a comment.
When iGTD was last updated, it started dropping data. The author did not reply to my inquiries. Recommend to stay away from this one.