I tried just writing it down on a scrap of paper that I kept on the side of the tank when I got my first snake, then I went a short period where I just marked the days they ate on a calendar.
Last year though, when we became really serious about breeding, I created a chart in excel that I used to track feedings, sheds, and health issues. This year I enhanced the charts to include all of the breeder info, genetics, weekly/monthly weigh-ins in addition to any health problems, feedings, and sheds.
I have both a hard copy where I write everything in manually so I can see each snake's records as we feed/weigh etc.. and then every couple of days I update the electronic versions of the files on the computer. I keep the charts on card stock in a binder, but can print a plain paper copy to go with any snake we sell in the future.
I didn't know there were actual programs out there that were created for just that purpose, and I imagine they are well put together and easy to use. I guess each person/owner/breeder has a different preference, and uses what works best in their opinion.
Jenn