Well, just two programs, at present, for free download.
The Daily Journal manages daily notes, appointments, alarms to upcoming appointments, contacts, holidays and to-do list.
The latest version is written using Qt, while the earlier versions were using FLTK.
Treecle is program for creating, managing and maintaining treelike heirarchical data.
Click this link to download The Daily Journal 3-0.2
Click this link to download The Daily Journal 2-0.4
Click this link to download Treecle