Ladybird got like at least 250k in funding last year by Shopify. The project refuses to release binaries so you'd have to build it yourself. So far the team has completed a JS engine from scratch and hit a 100/100 on the acid3 test.
Servo's earlier in development but its got some preliminary stuff. They have a few full time devs. The project is written in rust so its getting a lot of hobbyist support too. Their main project is getting CSS compatibility.
Flow is a closed-source browser by some company. Their browser is in beta right now but as evident by this paragraph I don't know much about its project.
Idk how to check commit numbers on mobile but I'd say all 3 are in the thousands minimum.