I'm very lucky to have two co-founders who are both much better at sales and business development than I, so one of them handled the details... But my recollection is that they approached us with a very vague idea that we were doing good stuff and maybe we can work together somehow? First instinct might have been to try to sell them ads (we're fully ad-supported), but after talking to them what they really wanted was 1) ways to provide more value to their members, 2) ways to do internal promotions to existing members and 3) things that are really easy for them to execute. So we racked our brains and came up with a deal where we write, manage, and send a weekly email newsletter with content tailored for their audience. The newsletter has both our logos in it and we promote it to our larger audience. They have a section they can use to promote their own events and content, and we promote the newsletter to our larger audience. We also provide discounts on ads to their members.

It's not the sort of deal that "easy" in that it took real work to put together. But I think it's worked out great for everyone.