Budgeting SaaS product Actual went open source and can be self hosted
Adobe is buying Figma, Penpot is an alternative
Komikku, A FOSS manga reader
Some alternatives if you don't read strictly manga (from It's FOSS)
Conor has tried Mcomix and it seems to be a great lightweight comic reader that supports the features that you would want it to
yarr RSS reader
Some Firefox add-ons (from It's FOSS)
New browser written completely from scratch, by the author of SerenityOS