What can “Tell HN” include?

Largely whatever the author chooses. What survives HN's automatic penalty (no-link posts get lower ranking than those with a link) and the submission queue rely on the interaction with the moderating readership at the time of submission.

There've been 319 front-page "Tell HN..." stories through 21 June 2023, of 178,882 total stories (I have an archive of front-page stories), with a random sampling of 30 of those being:

  Tell HN: Catch.com raises 7m. Didn't get in as solo founder (S08), kept pushing
  Tell HN: Coming soon – “Meet the Batch” threads for parallel Launch HNs
  Tell HN: Wells Fargo completely offline
  Tell HN: You guys scared edw519 off Hacker News
  Tell HN: Read Maxim and other trashy "guy" rags.
  Tell HN: Doing a PhD is good
  Tell HN: Thank you whoishiring, a.k.a. Matthew Walsh-Cloonagh
  Tell HN: We just launched GeoAPI.com (read/write geo API)
  Tell HN: just made my first dollar on the Internet from my freemium web app
  Tell HN: Rails screencasts.
  Tell HN: A $40B company killed my 2yo son. Now they force me to keep silent
  Tell HN: Interviewed with Triplebyte? Your profile is about to become public
  Tell HN: A disabled 40-year-old person founded a startup and makes a living
  Tell HN: Amazon fraudulently canceling orders as returned items
  Tell HN: Stop surfing and start making things people want
  Tell HN: I think I'm quitting my job today
  Tell HN: The 10-bit timers are about to overflow on September 17th
  Tell HN: Guess what Baidu and Yahoo China have already censored?
  Tell HN: Do not store any funds in PayPal or use them for anything critical
  Tell HN: Instagram demands I send a picture of myself to prove I own my account
  Tell HN: Let's Be Civil
  Tell HN: I wrote a website with a unique method of recommending links.
  Tell HN: Social media strike proposed for July 4-5 by Wikipedia co-founder
  Tell HN: YC Application Responses Are Out
  Tell HN: Cloudflare Is Blocking Piped
  Tell HN: My startup is making money and I don't know what to do
  Tell HN: The 2 best things I love about HN
  Tell HN: Summary of HN User Directories
  Tell HN: AWS warns us about irregular activity related to Log4shell
  Tell HN: Take vacation

(A random sampling should afford an unbiased view of what has made the front page in the past.)

Breakdown by year:

   9 2008
  51 2009
  60 2010
  19 2011
   9 2012
   7 2013
  13 2014
   8 2015
   7 2016
  10 2018
  11 2019
  13 2020
  19 2021
  62 2022
  18 2023

The "Ask" posts can be accessed by navigating to /ask and the "Show" posts can be accessed by navigating to /show. "Tell" isn't official, just something people type. No real guidelines to it as far as I'm aware.

Anything that you have created that you want to share and can spark interest or debate. Say an application of some sort, a blog, some cool hack.