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Tom Preston-Werner, a co-founder and former chief executive of GitHub, a website for sharing and collaborating on software code, resigned on Monday after an investigation into gender-based harassment. But the company said the investigation found no evidence of illegal practices.

The accusations surfaced last month, when Julie Ann Horvath, a software designer and developer at GitHub, publicly resigned, saying there was a culture of disrespect and intimidation of women at the company. That included mistreatment by Mr. Preston-Warner and his wife, who was not a GitHub employee. Ms. Horvath’s resignation attracted much attention in the tech community, as an example of the sexism and alpha-male culture that are endemic in software engineering.

“The investigation found no evidence to support the claims against Tom and his wife of sexual or gender-based harassment or retaliation, or of a sexist or hostile work environment,” Chris Wanstrath, GitHub’s chief executive and a co-founder, wrote in a blog post on Monday. “However, while there may have been no legal wrongdoing, the investigator did find evidence of mistakes and errors of judgment.”

He added that GitHub was starting initiatives led by employees and the human resources department to try to make it a more inclusive workplace and to ensure that employee concerns were dealt with appropriately. “We know we still have work to do,” he wrote. Despite being founded in 2008, GitHub hired its first senior human resources executive this year.

Ms. Horvath responded to the announcement on Twitter. Among other posts, she wrote, “Bullying someone into quitting: Illegal,” “Pushing women with strong opinions out of your company because they disagree with you is wrong” and “Leaving GitHub was the best decision of my life.”

Mr. Preston-Werner on Monday wrote that he had “made mistakes” but added, “We are prepared to fight any further false claims on this matter to the full extent of the law.”

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Ms. Horvath is a prominent figure in the movement to change the culture for women in tech. She started a program called Passion Projects, at which a technical woman presents her work in San Francisco each month. GitHub had sponsored the project but signed it over to Ms. Horvath when she quit. She is restarting it within a new organization called Playing with Possibility and expanding to New York and Chicago.

Women, who account for only one-fifth of software engineers, are even more outnumbered in open-source software. Ms. Horvath was the only female developer at GitHub when she was hired, and just 2 percent of people in the open-source software field are women.

GitHub, which has raised $100 million from the venture firm Andreessen Horowitz, has had considerable success, brashly illustrated by the elaborate bar and mock Oval Office at its San Francisco headquarters.

Marc Andreessen, the well-known founder of the venture capital firm that financed GitHub, was among those that rallied behind Mr. Preston-Werner on Monday:

We stand firmly behind both Github the company and Tom the person — we know that both Github and Tom have very bright futures ahead! — Marc Andreessen (@pmarca) 21 Apr 14

Reaction elsewhere in the tech community, however, was swift and negative.

GitHub is apparently just another corporation that has decided dudebros are worth more than other employees. — Patrick McCulley (@panther_modern) 21 Apr 14

I don’t understand how you can’t find evidence of sexism when sexism is institutionalized. #Github — Matthew Dean (@matthewdeaners) 21 Apr 14

THIS IS WHAT WE MEAN BY HOW THERE ARE NO CONSEQUENCES FOR WHITE MEN IN TECHNOLOGY. NONE. ZIP. NADA. — Shanley (@shanley) 21 Apr 14

Quentin Hardy contributed reporting.