Over the last few months I’ve been able to see a few different websites utilised during retros:
https://www.sli.do this site allows you to do Q and A’s, word clouds, voting up and down popular topics, polls and much more. Features free options and paid plans.
https://funretro.io/ allows you to create boards for mad, sad, glad (for example) and the team can add cards to each column, vote up or down add comments and more. I’ve not seen this one used as much but its definately something to look in to. Free options and paid for plans.