Agency offers free business tools, ideal for cross-promotion

The OP's agency has created a few handy free tools—a real-time invoice generator, a bulk QR code generator, and a color palette extractor—and they're available on their website. These could be great for collaboration, like featuring them in a "best free tools for small businesses, freelancers, or designers" article or newsletter. If the collaborator's audience is a good fit, they could highlight these tools, offer a reciprocal feature, or even explore a partnership. This way, the OP's agency gets more traffic and potential leads, while the collaborator provides valuable resources to their audience.