In Sid Meier's Alpha Centauri (SMAC), the Nano Factory is a Secret Project. It may be built at a cost of 400 minerals, on discovery of Industrial Nanorobotics (B9). Normally your units repair at 10% per turn of inactivity, and can't repair the last 20% of damage, outside a base. The Nano Factory allows your units to repair rapidly and fully with a turn of inactivity even outside of bases. It also reduces the cost to upgrade obselete units to new designs by 50%.

How useful is this? As your faction discovers the prerequisite technologies, you gain no less than 20 total potential weapon and armor upgrades. It's somewhat cheaper to upgrade military units than produce replacement garrisons and invasion units; this Project makes it that much more economical. The rapid repair is quite valuable as well; base garrison units become more likely to survive repeated attacks, and your enemy will have less opportunity to finish off your damaged attacking units. With the Nano Factory, you need less military in the field, because they can withstand more combat over several turns. I estimate that the Project doubles the value of garrison and assault units, above and beyond the savings in upgrade costs.

Secret Project animation narrative:
   "Industrial Grade Nano-Paste, Planet's most valuable resource, can also be one of its most dangerous. Simply pour out several canisters, slide in a programming transponder, and step well away while the stuff cooks. In under an hour the nano will use available materials to assemble a small factory, a hovertank, or enough impact rifles to equip a regiment."
   -- Col. Corazon Santiago,
   "Planet: A Survivalist's Guide"