Thunderbird # already has a great support for VTODO VCALENDAR and contacts. What is missing though is support for VJOURNAL entries. Journals are close to calendar entries. A great vesoverview gives jtx Additionally they introduce "notes" which are simply journals without a date.
The open source calDAV and cardDAV is a great way to share information between groups and family. Journals and notes would complete this sharing nicely.