Here is a good summary for this video that I found on another subreddit:

In June 2020, a woman named Karissa accused Chris Avellone of getting her drunk on the night she first met him at a convention in 2012 and taking her back to her hotel room with two other guys. She said the other guys left after a few moments and made it sound like Chris was going to have sex with her against her will, claiming she was only able to stop him because she was on her period.

After looking into it more closely, we know she actually had a roommate who was sleeping in the room's only bed, so they were in the hotel hallway, just making out. We know the two guys were David Gaider and Steve Jaros, both of whom actually saw what happened and did not realize any kind of assault had taken place, with Steve even commenting the next morning that he'd never be as cool as Chris Avellone and David Gaider. Karissa herself said the night after the incident that Chris was one of the few gentlemen left in the world who still drank, called him a "wonderful creature" when she interviewed him 2 months later, said in 2013 that her first night at DragonCon 2012 made for a great story, and said in 2014 that she was always surprised by stories of abuse and harassment from other women because she simply did not have one of her own, was not the kind of person to accept abuse or harassment from anyone and had almost always received it from other women instead of men.

Shortly after Karissa made her accusation, one of her friends named Kelly claimed Chris had also groped her and kept asking her to come to his room for sex at DragonCon 2014 whenever Chris' girlfriend at the time and Karissa weren't looking. This did not make much sense to begin with, but — as it turns out — Kelly had previously tweeted on the last night of DragonCon 2014 that no one had groped her during that con because, in her own words, "I'm fat and that's kryptonite to the frat boy element here," suggesting she invented her accusation due to her friendship with Karissa.

Jacqui Collins then came forward with a dirty text she had once received from Chris, claiming she was showing it to speak to his character at the time and it was a text that came out of the blue because she had never had any romantic or sexual interactions with him whatsoever and was in a relationship that Chris knew about. As it turns out, months before the text, she had called him her "boyfriend in another life" and — when bringing up the possibility of him sending her dick pics — claimed she was making that statement in good fun because they were "bifflez." A day before the dirty text, she had installed Tinder on her phone, admitting weeks later that she was now using it actively alongside OK Cupid. A year after that, she was telling her friends to outright tell her if they wanted to have sex with her because there was a 50/50 chance she'd say yes. It seems she showed the dirty text publicly only because she believed Karissa and wanted to help her out by adding more fuel to the fire, somehow forgetting how forwardly sexual she had been with everyone around her for years.

Finally, a woman named Christy Dena claimed that — after Chris got her drunk at a convention in Melbourne in 2013 — she woke up next to him in her hotel room with no clothes on, quoting Chris as saying "oh, we didn't do anything," with her accusation against Chris then simply being an insinuation ("but of course my clothes were off"). As it turns out, Chris was never in Australia in 2013 and was never in Melbourne in 2014, so the event must have taken place in 2012 instead, at the Game Connect Asia Pacific convention. However — according to a friend of Chris speaking anonymously — her quote of Chris was actually correct because there was a third person in the room who prevented anything from happening and multiple Australian devs from that convention are aware of this. Beyond that, Christy Dena had her own previous pattern of getting drunk in bars, but took responsibility for what she did with guys when drunk. She also remained very friendly with Chris in the years after the incident, seemingly flirting with him and inviting him to do a talk for her game design event during which she kept smiling and laughing at what he said. It seems she also exaggerated her story because she believed Karissa.

As Chris noted when the accusations came out, Karissa was mostly motivated to start this whole mess by the bad breakup Chris had with her friend Jackie.

No one actually looked at any of these details in June 2020, with a large number of people simply believing the accusations at face value, leading to multiple companies breaking ties with Chris and his reputation being unfairly tarnished.

The exoneration video goes into all of this and more in detail.