I recently found out about Dash, which turned out to be an unexpectedly efficient productivity booster. It has an awesome snippet mechanism, but the main selling point for me was the instantly-invoked, HUD-style documentation browsing.
Suprisingly, I could not find good equivalents of Dash on neither Windows nor Linux, which is a shame. Nevertheless, if you use a Mac, I urge you to give it a try, it keeps on saving me lots of time and context switches when browsing documentation, especially those pesky-apis-you-use-seldomly-and-never-remember-which-argument-goes-first.
@kapeli, creator of Dash, is accepting requests for docsets to be included in Dash's repository, and he maintains a voting system for deciding which docsets get published next. He's done an awesome job building the tool and providing the many docsets he already does.
Still, working with many Python modules and packages on the day-to-day I decided I could use a few extra ones that perhaps no one was yet to request besides me, so I decided to host them myself. The index to the repository is here. Feel free to contact me if you have any question, request or feedback via @vmalloc.