Technology for Big Planet
There's a moderately-common scenario in SF stories: a planet with a nearly-complete lack of iron and other heavy metals. Examples include: Big Planet by Jack Vance, The Man Who Counts by Poul Anderson, The Riverworld series by Philip José Farmer, Tatja Grimm's World by Vernor Vinge. This lack of metals makes it very difficult to start up a technological civilization.
I've been wondering if it is possible to start up a technological civilization on such a world anyway. For example, I think it might be possible to build Stirling engines out of nonmetals. Electricity might be more difficult but it should be possible to make an electrostatic generator. Graphite is somewhat conductive, so given an electrostatic generator and graphite bus bars it should be possible to make an electrolytic cell. The electrolytic cell, in turn, makes aluminum possible.
In short, it should be possible to have at least a mid-20th-century level of technology.