Best free game to speedrun
https://www.speedrun.com/games#platform=Web&orderby=mostactive&unofficial=off
99% of webgames are free to play, by going to this link ^^ you can see what free games are most popular for speedrunning
https://store.steampowered.com/app/1559930/Dialogue_Box_The_Road_Less_Traveled/
Free beta, has speedrun mode