First off, you have gensplosion in the wrong place - it should be in multifandom at the top, as it is a reccing comm like fancake and het_reccers, only for gen fic, not a creative comm for posting gen fic.

Seasonal
halfamoon - first fortnight in Feb, celebrating women in fandom, with daily prompts.

naarmamo - annual August 'National Art Making Month'

Specific fandoms:
OUaT abc_onceupon (although also ouat which was being used up to the end of the last year) - general comms I believe there is still an active Emma/Regina comm as well.

The Librarians thelibrarians_tv

Timeless timeless_lifeboat


Exchanges/fests I didn't see above, although apologies if I missed them!
fic_corner - exchange for children's lit fandoms (runs every other year, so could look inactive when it isn't)

genex - gen exchange

unconventionalcourtship - multifandom annual ficathon for fic written using Romance novel summaries

everywoman - multifandom exchange for female characters

remixrevival - Multifandom Remix challenge/exchange

history_exchange - exchange for historical RPF

multifandomdrabble - multifandom drabble exchange


Another general one - historicalyafen - for all discussion & fanworks relating to historical YA books.