A small Openismus task I recently carried out was to investigate whether there is a generic timeline widget for GTK+ out there, for example to show photos associated with the day they were taken. The main feature this is supposed to have is that the items it contains are grouped by time periods, such as day, week or month, and that it should be possible to view multiple periods at once, or to allow easy browsing between them.
The closest thing I found is Gnome Zeitgeist, an application which takes up Federico's Journal Idea. Gnome Zeitgeist is still under heavy development (I also had a short look at it yesterday, and when I updated the branch today it looked totally different), but the timeline widget looks promising already. It shows recently used files ordered by the day they have been used. By default, it shows three days, but when filtering by tags, it can also show more (scrolling horizontally if necessary), omitting days with no entries at all. This is implemented using multiple GtkTreeViews, therefore I guess it would be easy to generalize the widget to show arbitrary data by allowing to pack own cell renderers into it.
Then, there is Nemo, a program which aims at making file management easier by showing all documents (not only recently used ones) in a calendar type of view. There are views for a day, a week, a month or a year. However, when there are more items than there is space in a calendar cell, then it simply shows "+ 309 more". Gnome Zeitgeist allows scrolling instead, which is more handy when for example previewing photos.
Other projects I had a look at include Gnome-Shell (which shows recently used icons ordered, but not grouped), Wizbit (which has a timeline widget for the revision graph, but Wizbit has slightly different usecases), Paperbox and tracker-search-tool (both of which don't group items by time periods).
The Gnome Zeitgeist widget looks really promising, though. Although it is not a stand-alone widget, I don't think it would be too much work to separate it and make it more generic.
Are there more solutions to this kind of problem in the GTK+ world? Any application I did not have a look at, although I should in this context? If so, please tell me in the comments.