A seasonal calendar of recurring game jams, blogging prompts, design competitions, and challenges to spur your work on narrative and tabletop games.
This is fairly extensive (but necessarily incomplete). It includes board games, RPGS, storygames, and interactive fiction. I have deliberately excluded game jams focused on graphical video games, but if that's your jam (HA) then you can check out the calendar at Indie Game Jams. I've tried only to include -active- competitions that have happened more than once. There are loads of new game jams on itch.io going on all the time as well--and Max has a collection of current physical game jams on itch. I've guessed at the likely date of some competitions based on previous years. Some long-running competitions have ended or are no longer updated, but have extensive archives of games worth looking at--they are listed at the end.
(Also, someone should host another Threeforged because that was a great idea, and the One Room Game IF Competition was great and should come back in some form.
Do let me know if I've missed any regular things!
ONGOING / TRY ANY TIME
The Gygax 75 Challenge https://rayotus.itch.io/gygax75 (make an rpg campaign setting in 5 weeks, working through a booklet)
RPG Blog Carnival https://ofdiceanddragons.com/rpg-blog-carnival/ (monthly topics hosted by active bloggers)
Meta Prompt Generator https://crateredland.blogspot.com/2020/07/meta-prompt-generator.html (write an rpg post about...)
Game Crafter Community Contests https://www.thegamecrafter.com/contests (boardgames, roughly every 3-4 months)
One Month Story Challenge http://howtomakeanrpg.com/a/one-month-story-challenge.html (nobody has used the hashtag since 2015, but the challenge is self-guided for creating a bunch of narrative ideas)
WINTER
Secret Santicore/Santicorn http://santicore.blogspot.ca/ (OSR rpg content, now mostly run on the OSR Discord but archives up to 2017 still online. 2018/2019 collected on various blogs)
SPRING
Spring Thing (Mar 1 deadline, submit by Apr 1) http://springthing.net (interactive fiction)
Secret Jackalope (an Easter-ish version of Secret Santicorn for OSR rpg content)
SUMMER
RPG Superstar (deadline June) https://rpgsuperstar.com/ (rpg content design competition)
IntroComp (deadline Jul 31 but pre-register in Jun) http://introcomp.org/ (first room of an interaction fiction)
#RPGaDay (August) https://melestrua.wordpress.com/category/rpgaday/ (daily prompts for blogging/game design)
Saga Forge Scribe (August 24 deadline) https://www.wearesaga.com/sagaforge (one-shot module competition, Halloween theme)
200 Word RPG (did not run 2020 but claims it'll be back) https://200wordrpg.github.io/
(and ongoing submissions at reddit.com/r/200wordrpg)
AUTUMN
The Mega RPG Jam (ran in Sept 2019) https://itch.io/jam/mega-rpg-jam/community (creator says will be another one in 2020)
IFComp (deadline Oct 1 but pre-register in summer) https://ifcomp.org/ (interactive fiction)
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DEFUNCT (but archives available)
BGDF Game Design Showdown http://www.bgdf.com/forums/game-design/design-contests (last thread was posted august 2018)
XYZZY Awards http://xyzzyawards.org/ (last awarded for 2018)
New Year's Minicomp https://intfiction.org/t/eleventh-hour-new-years-minicomp/12848 (last ran in 2017)
Game Chef (no archive or website anywhere! I just thought I should mention this great little competition that appears to have completely vanished)