pokoy is lightweight daemon for X that helps prevent RSI and other computer related stress. It locks the screen and forces you to take regular breaks. Pokoy doesn't have any dependencies except xcb and consumes less than 2 mb of memory. See man page for more information.
Building and installation:
$ make
# make install
Examples:
$ pokoy -r # run daemon
$ pokoy
29:59
04:59
$ pokoy -s
$ pokoy
Daemon is sleeping.
$ pokoy -s # wake up
$ pokoy -n # start first break now
$ pokoy -k # kill daemon
Screenshot: