The technology level (or "tech level" or "TL") describes the general level of technology that a system can manufacture. The system may be able to repair technology from a higher TL, provided that it has access to replacement parts and skilled technicians.
The TLs in this game are based not only on how human technology has progressed historically (which is hard to generalize because, e.g., Europe and East Asia followed different paths). TLs are also derived by thinking about how a colonized planet might regress. In other words, what are likely to be the key barriers between different levels of technology? For example, if you have AC electrical power, you can probably make integrated circuits and a global communication system, even though on Earth it took more than 100 years to go from Nicola Tesla to Facebook. At the same time, building and maintaining megawatt generators and silicon chip factories require a certain industrial base to support them. Ultimately, these are guidelines and generalities—individual planets can and do vary from these "base" levels for any number of reasons.
The following TLs are inspired by those in GURPS 4e and the Stars without Number core rulebook.
0: Pre-agrarian stone age
1: Agricultural revolution
2: Bronze age
3: Iron age
4: Middle Ages and Renaissance
Telescopes and lenses
Plate armor and siege weapons
Navigation instruments
Gunpowder
5: Industrial revolution and steam power
6: Age of electronics
Transistors and basic electronics
Electrical power distribution
Powered flight
Nuclear power; atom bombs
7: Digital age
Integrated circuits
High speed global communications networks
Early spaceflight
Thermonuclear weapons
8: Twenty minutes into the future
Machine learning and specialized AI applications
Neural interfaces and early cybernetic prosthetics
Nuclear fusion
Rudimentary or coarse genetic modification
"Wet" nanotechnology and organ printing
Vehicular directed energy and electromagnetic weapons; Gauss needle-guns
9: Just over the horizon
Fusion rockets
Fine-grained genetic modification; anti-aging treatments; augmentation beyond normal human abilities
Identification and training of psionic abilities
Non-volitional AI
Antimatter rockets and power sources
Small scale nanotech printers
"Smart" matter
Molecular manufacturing
Man-portable directed energy and electromagnetic weapons