I haven’t done concurrent brews, but like others I’ve done overlapping. I don’t usually do it though. My brother and I did three 5 gallon batches on a Saturday. It was a long but successful day.
I also do parti-gyle batches for my big brews. First runnings for the big beer. Second runnings for the small beer. If you have a 2nd boil kettle you can have the second runnings boiling within 15 minutes of the first.
I’ve done three in one day and five in 24 hours !:o I’ll never do that again!
I have done two in one day with my equipment (2 burners and more than one MT) while helping my neighbor learn to brew. We did a 12 gallon batch and a 10 gallon simple pale ale for him, staggering the steps so that when my boil was starting his sparge was going. It was hectic, but mainly because it was an unplanned second batch. I have also collected second runnings and made 5 gallons of small beer following a 10 gallon batch of stronger beer on more than one occasion. I am not usually pleased with the small beer, but second runnings are also a good way to get a batch of starters out of the way.
in what ways? I was thinking of partigyling my barleywine at the end of the year, throwing a few more pounds of basemalt and half pound of crystal to brew an ESB of sorts with the seconds - please explain further. perhaps another thread is in order as to not hijack this one…
[quote]It’s pretty common for me to do a 10gallon batch, and then split it into two 5 gallon fermentors at the end.
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That is MO these days. I like being able to try two yeasts or dry hop one and not the other, or just make 10 gallons of a tried and true session beer (Starter for Fred.)
I usually brew 2 batches simultaneously. Extract batches boiling on a stovetop 
My record is brewing 5 in one day - 2/2/1. No problems at all.
That’s what I’ve been thinking about doing, but I think I would still need second burner to get the sparge water ready.
I often do multiple batches with multiple tuns. An even easier method is to split the wort and do separate boils to end up with two different beers. Another fun thing is to water one down post boil to end up with a stronger beer and a lower abv beer. Think IPA and PA, Alt and Sticke, etc.
I’ve done 2 batches in one day several times, but it’s a ton of fun/work. The last time I did it I brewed 10 gallons of Bohemian Pils and 15 gallons of brown ale split into 3 buckets with different yeasts.
Two batches at once? Sort of. I plan to do a partigyle next Saturday. 1st runnings will be a Strong Scotch Ale in the 1.090 range. 2nd runnings (with 5 more pounds of grains) will be a 70/- to 80/- Scottish Ale depending on the SG. The Strong Scotch Ale boil will overlap the Scottish Ale for a half hour or so. Started the Wyeast 1728 today. I’ll step it up to a gallon through out the week. It’ll be a big day for an’ ol’ fart like me :o but the rewards should be worth it.
I have access to 2 large kettles, 3 mash tuns and 3 burners. I routinely do 2 batches with this set up. I just stagger start my batches by about an half hour. Same amount of work really to get twice as much. I will also do a parti-gyle with the same grist in 2 mash tuns. I take the first runnings of each for a strong ale (10g) then the second running for a standard(10g). If I am really good I can get a third 5g small ale as well. takes about 10 hours to get it all done but I am finished for the month. One brew day for what used to take 4 weeks. More time for drinking since I am lazy and keg now.
Yes… I have 2 systems, one where I can do 15 gals and one where I can do 45 gals. On the larger one I can
split the wort between 3 kettles, one 30 gal and 2 x 15 gal so I can hop 4 different scheduals/bitterness/flavors.
When I chill I sometimes mix it up in the carboys by soaking special/dark grains to take a base beer even farther,
it just depends how much work I want to put in it.
Max output for one of these brew days is 12 carboys, but it is a lot of extra work before and after - sorting/grinding grain,
sorting/weighing hops and getting all the timing correct… plus all the carboys and yeast pitching !
I can also pull off 2 different types of beer by using first runnings only and batch sparging to get a small beer… this could be
lager or ale, Belgian, Barley Wine, Imperial beers…
Pulling off the big brew day usually adds 3 hrs on top of my normal 6 hr single brew day so it is pretty taxing especially if your having a few pints during 
We always make two batches at the same time. My wife makes one while I make the other. When she is not available to brew, I will make them both myself. Occasionally I do get things mixed up, usually late hop additions. We have a Y adapter on the water line so that we can run two chillers at the same time. That works fine.