The Crowners were the first particularly elaborate technical alteration made to TV Tropes for purposes not relating directly to wiki maintenance. They were created with a simple purpose in mind- to quantify the trope Crowning Moment of Awesome.
Crowning Moment of Awesome by its original definition was theoretically supposed to refer to an individual series moment which summed up everything that made the show great. Hence the use of the word "crowning". However, it soon ran afoul of the wiki's hive-mind interpretation. People at large who saw the entry and how it was used on the wiki did not think about the grammar of the phrase, and how technically any individual series could only ever have one "crowning moment". They simply thought "oh, this must be a trope that means 'something really cool happened'". Unfortunately, "something cool that happened" isn't really a trope. It's completely subjective based on personal experience. Pretty much anything could be that trope depending on your perspective.
The denizens of TV Tropes were not particularly interested in this constructionist interpretation of trope meaning- they latched on to the new idea of the Crowning Moment. Other crowning tropes were proposed and added to the wiki, and the label pretty much became a predicate that meant "something which inspires great emotion".
In an effort to solve this problem without angering the entire wiki, the crowners were proposed. The crowners are simple voting software. The idea behind them was pretty simple- rather than have multiple, nonsensical Crowning Moments of Whatever, everyone simply votes on the one they like the most, and that is the Crowning Moment.
It was a reasonable enough idea, but it failed in multiple ways to measure up to reality. Most tropers had no idea the crowners existed after implementation- few used them compared to the number of wiki readers at large, and while this was going on, examples continued to be added to pages which were by definition incorrect because a series can only have one "crowning" moment of anything. What it got right down to was that people didn't come to TV Tropes to vote about what their favorite scenes in a show were- they wanted to write about them. The admins eventually had no choice but to give up in this matter entirely, closing the original crowners and creating a new namespace on the wiki specifically devoted to cataloging the subjective content the wiki proper so badly wanted to write down. At this point the inaccurate term "crowning" was removed from the names, so at least it was technically accurate.
In retrospect the whole thing was really a missed opportunity. The Crowning Moment pages were just an excuse for many users to write about their favorite moments in a series. The thing is, tropes are quite literally everywhere. Had we tried encouraging tropers to instead build YKTTW proposals out of examples that they wished to make Crowning Moment entries for, the whole enterprise could have gone in a much more constructive direction.
That, of course, is being a bit unfair on the past. This idea was floated back when the very idea of semi-centralized Trope Repair was quite primitive and people still didn't have much idea how things worked on the wiki pragmatically. I personally failed to see the importance of these issues at all at the time. I only know what happened at all because I went back and studied the discussions back when the crowners ended up becoming relevant for very different reasons. In part, my general apathy toward this issue is why I'm unsure of the exact dates in which these events occurred. I played a very direct part in the other major usage of the crowners, so my exact reflections and interest on their original purpose don't weigh quite so well on my memory as their second one.