diff --git a/lib/DataStore.py b/lib/DataStore.py
index ee69298..23ac5f9 100644
--- a/lib/DataStore.py
+++ b/lib/DataStore.py
@@ -9,7 +9,7 @@ class DataStore:
         if create:
             # Store emtpty list
             self._time_slots = []
-            self._write_update()
+            self.write_update()
         else:
             # Load dicts from file
             with open(self._filename, "r") as f:
@@ -23,18 +23,18 @@ class DataStore:
 
             self._time_slots = [deserialize(d) for d in self._time_slots]
 
-    def _write_update(self):
+    def write_update(self):
         """Saves the updates made to the DataStore object to disk."""
         with open(self._filename, "w+") as f:
             json.dump(self._time_slots, f, default=vars)
 
     def add_time_slot(self, time_slot: TimeSlot):
         self._time_slots.append(time_slot)
-        self._write_update()
+        self.write_update()
 
     def remove_time_slot(self, time_slot: TimeSlot):
         self._time_slots.remove(time_slot)
-        self._write_update()
+        self.write_update()
 
     def get_all_time_slots(self):
         return self._time_slots[:]
diff --git a/lib/TimeSlot.py b/lib/TimeSlot.py
index 7780d3c..0241dca 100644
--- a/lib/TimeSlot.py
+++ b/lib/TimeSlot.py
@@ -37,3 +37,6 @@ class TimeSlot():
         if d < self.start:
             raise ValueError("End date must be after the start date.")
         self._end = d.timestamp()
+
+    def end_now(self):
+        self.end = datetime.now()
diff --git a/main.py b/main.py
index ca131ab..c334a5b 100755
--- a/main.py
+++ b/main.py
@@ -6,15 +6,59 @@ from lib.TimeSlot import TimeSlot
 from lib.ui import convert_to_table
 
 
-if __name__ == "__main__":
-    parser = argparse.ArgumentParser(description='Time tracker')
-    parser.add_argument('command', type=str, help='Manage time slots.', choices=['start', 'stop', 'add', 'ps', 'ls'])
-    parser.add_argument('-b', '--begin', type=str, help="The start time of a time slot.")
-    parser.add_argument('-e', '--end', type=str, help="The end time of a time slot.")
+def create_parser():
+    # Create the top-level parser
+    parser = argparse.ArgumentParser(description="Time tracker.")
+    subparsers = parser.add_subparsers(dest="command", help="Sub-command help")
 
+    # Create the parser for the "ls" command
+    parser_ls = subparsers.add_parser("ls", help="List all events.")
+
+    # Create the parser for the "ps" command
+    parser_ps = subparsers.add_parser("ps", help="Show the currently running event.")
+
+    # Create the parser for the "add" command
+    parser_add = subparsers.add_parser("add", help="Adding a new event.")
+    parser_add.add_argument("-b", "--begin", help="Begin datetime")
+    parser_add.add_argument("-e", "--end", help="End datetime")
+
+    # Create the parser for the "start" command
+    parser_start = subparsers.add_parser("start", help="Starting a new event.")
+    parser_start.add_argument("name", help="Name of the event")
+
+    # Create the parser for the "end" command
+    parser_end = subparsers.add_parser("end", help="Ending the current event.")
+
+    return parser
+
+
+if __name__ == "__main__":
+    parser = create_parser()
     args = parser.parse_args()
 
     ds = DataStore("data.json")
 
     if args.command == "ls":
         print(convert_to_table(ds.get_all_time_slots()))
+
+    elif args.command == "start":
+        time_slots = ds.get_all_time_slots()
+        running = list(filter(lambda x: x.end is None, time_slots))
+        if len(running):
+            print("An event is already running.")
+        else:
+            ds.add_time_slot(TimeSlot(args.name))
+            print(f"Started event {args.name}.")
+
+    elif args.command == "end":
+        time_slots = ds.get_all_time_slots()
+        running = list(filter(lambda x: x.end is None, time_slots))
+        if len(running) <= 0:
+            print("No running event.")
+        elif len(running) > 1:
+            raise Exception("Found multiple running event.")
+        else:
+            running[0].end_now()
+            ds.write_update()
+            print(f"Ended event {running[0].name}.")
+