This drawing challenge entails identifying one thing you're bad at drawing (e.g. hands, machinery...), and draw 100 of that thing.
It seems to go back to a video on ctrl+paint.com
This is a drawing challenge running from July 1st to July 31st
What's the challenge? Draw animals from a prompt list that has one per day.
Where, how to take part: Find the prompt list (2018 at FB, 2018 at Twitter), draw, post to FB or anywhere using the tag "zoolyartchallenge".
This is an annual writing challenge running from May 1st to 31st (and sometimes September 1st to 30th)
What's the challenge? Write a finished story every day.
Official website: storyaday.org (warning: expect "sign up to my mailinglist" popups)
This is an annual drawing challenge running from November 1st to 30th.
What's the challenge? Draw an image in a different hue each day. official colour wheel
Where, how to take part: Post anywhere using the tag “huevember”
This is an annual drawing challenge running from March 1st to 31st.
What's the challenge? Draw a robots, ideally daily.
Where, how to take part: Post anywhere using the tag “marchofrobots”
Official website: marchofrobots.com
This is an art challenge running weekly.
What? Create an image based on the weekly theme posted on the official website on Friday
Where, how to take part: Post the image to your own gallery, submit a link at illustrationfriday.com
This is an annual writing-related challenge running from March 1st to 31st
What's the challenge? Spend a total of 50 hours editing a novel (such as last November’s NaNoWriMo manuscript)
Where/How to take part: Sign up on official page www.nanoedmo.com and track time spent editing there
This is a writing challenge running annually in April and July.
What's the challenge? Set yourself a wordcount goal and meet it.
Where, how to take part: Sign up on the official website, campnanowrimo.org
When? June 1st to June 30th
What? Draw an image based on a pose reference photo picked by senshistock for that day.
Where, how to take part: Watch senshistock on deviantart
2018 announcement - 2018 gallery
When? June 1st to June 30th
What? Create details of a world you are creating. Writing or art are welcome; there is a prompts list.
Where, how to take part: worldbuildingjune.tumblr.com