Paying taxes by work time

Currently, the state seeks only money from his citizens to perform its tasks. Which means that people who cannot pay money are a burden for the state. This would change radically if people are also able to pay their taxes by their work time. Or even better, if this is the default case. For example, one would contribute ones amount to the state (ones “community”) by doing a four weeks project in the summer that includes re-building and repairing highways. And IT people, for example, could pay their taxes by a dedicated amount of time they invest in open source software that will be used by the state. Ultimately, state would consists fully of people’s contributed work time, that is, would be indeed made out of its citizens.