Reddit is an American social news and discussion website. The homepage usesIBM Plex Sans for the link titles and most of the interface. The body text of posts is set in Noto Sans. Reddit’s logo uses a modified VAG Rounded.
Product logos that are part of the brand family like Reddit Ads are generally lockups of the logo with the product name in unmodified VAG Rounded. The alien dubbed Snoo goes back to a doodle made by Reddit co-founder Alexis Ohanian in 2005, see this post about the logo evolution.