According to a report by TechCrunch, Index Ventures has backed Slack competitor Quill. While that may not seem unusual in and of itself, it’s notable due to Index Ventures being a Slack investor.

Slack has taken the business world by storm, easily becoming one of the most popular office communication and collaboration platforms. At the same, it has faced criticism for being too “busy,” overloading users with notifications and direct messages.

Led by Ludwig Pettersson, Quill offers a more streamlined experience, focusing on “meaningful conversations, without disturbing your team.” It’s designed to offer more focused conversations, with an emphasis on threads.

Former Y Combinator president Sam Altman, who worked with Pettersson at OpenAI and led a previous $2 million round of funding, told TechCrunch: “It’s relentlessly focused on increasing the bandwidth and efficiency of communication. The product technically works super well–it surfaces the right information in the feed and it’s pretty intelligent about how it brings the right people into conversations.”

Quill’s latest round of funding, a $12.5 million Series A funding at a $62.5 million valuation, was led by Sarah Cannon, an Index Ventures partner and former Slack board observer.

Whatever Quill’s success, one thing is clear: Slack is facing increasing competition from all sides. Startups like Quill are rising up to improve on Slack’s perceived shortcomings, while established companies like Microsoft have competing tools backed by entire ecosystems of business software. Slack will have to continue to improve and evolve to maintain its position.