This advice will mostly be targeted towards those documenting libraries or frameworks intended for use by other developers, but much of it probably applies to any for of technical documentation.
RethinkDB is built to store JSON documents, and scale to multiple machines with very little effort. It has a pleasant query language that supports really useful queries like table joins and group by, and is easy to setup and learn.
FPC is a very fast lossless compressor with better results than most traditional algorithms:
FPC compresses linear sequences of IEEE 754 double-precision floating-point values by sequentially predicting each value, xoring the true value with the predicted value, and leading-zero compressing the result.