I usually only have 1 or 2 things going, so I don't really need a calendar to keep up with batches in progress. Right now I've got a Maibock in primary, and I know this week sometime I have to clean a keg and transfer it for continued lagering and in preparation for my next brew next weekend. I also have a mead in primary, and sometime around the 1st of next month I need to rack it to secondary before warm weather. Beersmith has a brew log and calendar function, and anytime I do something to a batch, I make notes in the recipe on my phone. It's real easy to go back and consult Beersmith with any questions about past brews. Each keg has a hang-tag or masking tape label with the name of the beer in it.
I find a calendar to be more useful when planning my upcoming brews than for keeping track of what needs to be done to past ones. I've got an empty keg or two to fill. Since I've got plenty of ales in the keg already and know I'm going to want a crisp, refreshing lager this summer, a pilsner is going to be my next brew, followed by a Märzen in March that I'll lager until end of September. If I kick a keg between April and then, I'll do either another pilsner or a Weizen because it's hot as shilt in Arkansas July-October and I don't want to be drinking a dark, heavy beer.
Any record keeping system you adopt needs to be simple and almost effortless. If it's too much trouble it'll eventually fall by the wayside. I do what I do because it doesn't really require anything extra and comes naturally. I used to keep a notebook a long time ago, but came to prefer software. Of course, when Promash became obsolete and I switched to Beersmith, that notebook came in real handy when trying to recreate my brewing history and/or recipes since Promash wouldn't even open up on my computer. Something still to be said for paper and pencil.