They can direct skilled people and material resources to where they are needed. They don't have to get involved with military projects. They can send skilled volunteers into schools and hospitals to train local people to take their places after a number of years. When you have successfully trained local people, they usually emigrate to countries where they are paid much higher salaries. There's always a risk of that .
Projects have to be carefully thought out.
You'd naturally try to select trainees with some commitment to their country. Anyway, it isn't such a bad thing to have dedicated volunteers working in the field. They can specify what equipment is lacking and this could either be supplied by donor countries or manufactured locally.