The HDA has a Calendar server ([http://en.wikipedia.org/wiki/WebDAV WebDAV]) enabled by default in Amahi 6 (Ubuntu 12.04.x).
This capability is currently broken in Amahi 7 ([https://bugs.amahi.org/issues/1339 Amahi bug 1339]). For Amahi 7 (Fedora 19) and future Amahi releases, you will need to install the Amahi [https://www.amahi.org/apps/calendar Calendar] application(soon to be released).
Using client software you can publish and also subscribe to published calendars on your HDA.