Only seventeen days have past since the last free weekend, and already Blizzard is announcing a brand new one. So if you somehow haven't given Overwatch a try, or if you have some friends you want to convert to the FPS side, you should schedule some free time from August 23-27 as Overwatch will be entirely free on PC, PlayStation 4 and Xbox One.
In terms of content, you'll be able to mess around with all 28 heroes (including the newly released Wrecking Ball), all 18 maps, all bazillion different cosmetics that hide within the loot boxes, as well as all of the various game modes including Quick Play, the Arcade and Custom Games. The only thing that will be locked away from you is Competitive Play, though that's not something you would want to jump in after only a couple of hours of playtime anyway.
As always, if you're on the fence, I would highly recommend you give Overwatch a chance. The balance has only been getting better over time, the new LFG tool has made it incredibly easy to find friendly people to play with, and there are plenty of unique heroes to choose from, regardless of your skill level and playstyle preference. So if you're even remotely interested in Overwatch or FPS games as a whole, this free weekend is a pretty good time to jump in and see what it's all about.
You can learn more about Overwatch, as well as check out all of the different heroes, by heading over to the official website. And finally, allow me to leave you with this somewhat tiny infographic showing the official starting times for the various time zones.