I have been keeping things low tech and use a 3 ring binder. I have a master list and garden maps. I hand draw the maps by making little circles with numbers for each garden and listing the plants along with their numbers. Now this is all I have been doing because I have very little time and to me, it's just easy to add new plants etc; to my lists.
But your question has me thinking. Up until now, I have had very few seedlings that matured enough to make it to the garden. Three exactly. So I know them by heart, how they bloom, what they look like, etc But that all changed this year. I have moved a large number of 2 crosses to the gardens from bins. I know where they are and what cross they are. But I need to keep track of when they bloom, health of blooms/plants and whether they have other redeeming qualities.
It may be time to start a spreadsheet.