What does Jane Street do?

Could you please elaborate on the primary activities and operations of Jane Street? As a financial services firm, I'm curious about the specific services they offer, the types of clients they cater to, and any notable achievements or distinctions they hold within the industry. Additionally, how do they approach market making and algorithmic trading, and how does their technology stack up against competitors in the field? Lastly, are there any recent developments or expansions that Jane Street has undertaken that are worth highlighting?