AO3+ by Gita

Search filters:
Multi-rating — select multiple ratings at once instead of just one
OR tags — switch tag matching from AND to OR so any tag match counts
Main ship — dedicated ship field with AO3 autocomplete; hides works where your ship isn't listed first
Default language — automatically pre-fills your preferred language on every search
Hide single-chapter — checkbox to exclude 1/1 works from results
Hide read — hides works you've already read, based on your AO3 history and link visits

Reading experience;
Reading time — shows estimated reading time on work blurbs and work pages
Words per chapter — shows average words per chapter on multi-chapter works
Chapter indicator — appends "Chapter X of Y" to the chapter title
Word replacer — replaces words/phrases inside a fic (managed in the popup)

Filtering & blocking:
Block lists — permanently hides works with certain tag, character, relationship, or author across all listing pages
Pagination — carries your custom filters through AO3's page 2, 3, etc. links

Saved searches:
Save search — saves search filters with a name; accessible from the popup
New works badge — shows a "+N" count in the AO3 header when saved searches have new works; dots new works on results pages

History:
History cache — indexes your full AO3 reading history in the background
History filter — adds search, fandom/ship dropdowns, and sort controls to your History page

AO3 Wrapped:
Yearly stats page: fics read, words read, estimated reading time, top fandoms, ships, and tags; with year selector and a "cap" note when the count exceeds the indexed cache