https://simple.wikipedia.org/ - as people who are (potentially) skilled at using a reduced vocabulary to explain complex things.
WikiProject Watches currently has:
Those 2 subreddits have thousands of subscribers, contributing to dozens of threads each day. There are experts and passionate amateurs in there, who enjoy sharing knowledge and helping newcomers. We are natural allies.
There have been a few bots over the years that detect comment-links to Wikipedia and reply with an excerpt. Including:
There are subreddits dedicated to
If you use the popular RES extension to enable fancy auto-expansion, the old (non-beta) design looks like this: http://imgur.com/u5II7JF
The hugely popular browser extension RES (RedditEnhancementSuite), has a feature that expands links to Wikipedia. (screenshot)
Code: https://github.com/honestbleeps/Reddit-Enhancement-Suite/blob/master/lib/modules/hosts/wikipedia.js (open issues)
NOTE: As of 31 January 2022, RES is in maintenance mode, which means no new features will be rolled out. See the announcement by the developers on Reddit