For who does not know, think Enterprise Integration, like Tibco or IBM MQ. Brokers, Adapters and all that. Still core at some large corporations.

If I am not mistaken, not by size, but by valuation metrics, still considered one of the most successful NASDAQ IPOs ever. Back in the crazy year of 2000:

"...In February 2000, webMethods had its initial public offering (IPO) on the NASDAQ exchange.Just before the offering, the share price rose from its planned $13 to $35, and in its first day of trading, closed over $212 per share. The company raised only $175 million, while being valued at almost $7 billion..."