A simple python application that periodically logs the name of the application you're working on.

applog.py

import win32gui, time, os.path

filename = os.path.join(os.path.dirname(__file__), 'applog.txt')
out = open(filename, 'a')
while True:
    title = win32gui.GetWindowText(win32gui.GetForegroundWindow())
    out.write(time.strftime('%a %d-%m-%Y %H:%M:%S') + '\t' + title + '\n')
    out.flush()
    time.sleep(30)