Another one is the water filtering 'straw'. It's a simple tube with many membranes of different sorts within. It's put around a child's neck on a ribbon. The child can dip it into any kind of water and suck. The thing filters to an amazingly tiny tolerance, and can cope with 800 litres of water, or a year's use.
I was at a Salvation Army Christmas Concert a few years ago, and at 'half time' a short talk about these straws was given, and a slide show, then the hat was passed round for contributions. At the end, they announced they'd raised over £2000! This would obtain no end of the filters for hundreds of African children.
It's another of my sister's pet charities, together with sanitary toilets of a special design for use where there's no running water. She often says she's the 'Toilet Queen'!
The thing is, in developing countries, complicated technology is no use. It can't be maintained, and cannot run on non-existent electricity. It has to be very simple and sustainable.