I was listening to a Podcast, The Joe Gardener Show with Joe Lamp'l regarding seed starting indoors. If you are interested in high density seeding indoors there is a three episode podcast on the subject.
https://joegardener.com/podcast/037-starting-seeds-indoors-pt-1/
The first podcast has seed starting expert, Craig LeHoulier, discussing his high intensity seed starting techniques where he puts up to forty seeds in one 1 1/2" x 1 1 1/2" cell.
The podcast has some updated information, the old Youtube videos show you the process. If you don't have a greenhouse or tunnel this is a great way to start a tremendous amount of seeds.
I was looking at the pile of seeds I have, trying to figure out where to put all of them. I am going to use this technique.