Dendron is more opinionated. It seems cool, but I didn't want to get too involved in a system.
Foam is just markdown with some vscode extensions. Foam is closer to obsidian.
It's similar and they are interoperable, but Dendron runs inside VS Code.
The implications of this cannot be overstated. Utilizing VS Code as a platform -- at least for a dev -- makes dendron feel intuitive and flexible enough to customize to my hearts content.