For very small (grams of thrust) rocket and jet engines the power consumption and weight of servos moving the gimbals become the performance bottleneck.
Therefore, does anybody have any ideas how to vector thrust by ideally electrical-only means? Of course, a set of engines pointed in different directions may do the task, but each need again at least one controlled mechanical valve (with the same scaling problems as with servos), so multiple-engine solution is not very attractive.