With the Kerbal Alarm Clock you can create alarms for the following situations:

Raw time alarms – created for either a specific date/time or a specific period in the future;
Manuever node – create an alarm based on the next maneuver node on the current ships flight path. This node will be stored and can be restored when you come back to the ship. You can now also set the alarm clock to monitor for maneuver nodes and create alarms as these are created New in 2.6.3. Now has threshold for auto adds;
Other flight path nodes – Apoapsis, Periapsis, Ascending Node and Descending node. These can be configured to track changes as they approach as well;
Launch Rendezvous – Alarm that can be set to fire as your landed craft passes under the orbit of your target New in 2.6;
SOI Point – create an alarm manually based on when the next SOI point is on the flight path, or set the alarm clock to continually monitor the active flight path and add alarms as it detects SOI changes (there is also a background check you can enable for ships to notice simple name changes in the SOI for any background vessel, but it will not slow time before hand and will miss the SOI change by a fair margin under warp);
Closest Approach – create an alarm based on the closest Approach of this Vessel to the targetted Vessel. Select how many orbits into the future to look for the closest approach;
Target Distance – create an alarm based on distance to a target vessel or altitude from the orbited (or next patch) planet New in 2.6;
Transfers- create an alarm based on Interplanetary Transfer Phase Angles – ie. When should I launch to planet X – Based on Kosmo Not’s post and used in Olex’s Calculator;
Crew- Set an alarm for a Kerbal so that you can come back to them after a set time – regardless of the vessel they are in New in 2.6. Now stores Taregts and Maneuver Nodes;
"Earth Time" – create an alarm based on the time in the "Earth" alternative Universe (aka the Real World);