T4D is real vocabulary. Technology for development, the sibling of ICT4D, is how a substantial part of the aid and development sector describes its own work. UN agencies use it, major foundations use it, and there are conferences and journals under the term.
That makes this three-character .org unusually well positioned. A development organisation, a foundation programme, a research centre, or a consultancy working in that space would get an address their entire professional audience already reads correctly. No explanation, no tagline needed.
The .org is essential here rather than incidental. The sector is nonprofits, multilaterals, and academic centres, and they use that extension almost without exception.
Other readings hold up for buyers outside development: tools for designers, training for doctors, transport for disabled. The 4-for convention is flexible enough to carry any of them.
Three characters, sitting inside a working professional vocabulary. Offers welcome.