This is a spectacular tool for handling ladder leagues, which they call "Shootouts".  The reason I love it so much is that it allows you to let people signup on their own, then games aren't scheduled until you're at the venue and have people are actually checked-in.  This means that no-shows don't affect you the way a more rigid league structure does.

They offer other random play format, but I'll admit that I haven't seen the utility there. If you enjoy Mix-It-Up or ABCD play at your club, I'd love to hear from you!

Finally, they offer league and tournament software. The costs there are higher than other options, and the UI isn't as refined, so I haven't used them for this. But seriously, the Shootouts are WONDERFUL!!!

The Dynamic Universal Pickleball Rating is an outstanding tool that both rates players very accurately, and has round robin software built-in for clubs.  GPC recommends that everyone get a free DUPR rating so that they can play skill-based round robins, even if they never want to play a "real tournament". 

Currently the event software is limited to single round robins with fixed partners. I like that players are assigned to brackets and seeded based on their rating. This gives me a good way to group people by skill, without anybody getting bent out of shape if you try to put them in a different bracket than they think they should be in. 

This is the gold standard. Everyone I know looks at this site first when trying to find tournaments. The user interface is extremely powerful, and yet not intuitive at all. 

This is a HIGHLY POLISHED site with tons of pickleball features, and it's FREE. Wow!  You'll have to advertise elsewhere, though, as you probably won't reach enough people through GPN alone to fill a tournament...unless you do small ones like me, then it's fine. :)

You can run leagues (with their own ratings calculator), but honestly the data entry is cumbersome enough that I much prefer Pickleball Den. 

You can run tournaments, and I've been very happy with the round robin tournaments I've run with this. I've not tried elimination brackets, though I'm sure they work smoothly, too. 

If you want a very traditional league (fixed partners, playing for a fixed number of weeks) then this is SPECTACULAR!  Seriously, the user interface is second to none. I LOVED using it. They aren't pickleball people, though, so the concept of rotating partners is lost on them, but for any traditional league, they're hard to beat!   They offer tournaments, too, but I've not tried this, and honestly I feel like a pickleball-specific tournament tool will do a better job (printing score sheets, etc.).