Where builders trade slices of what they built at 2am with Cursor.

Arjun had been building PromptLayer for eight months when he posted his first swap listing. He wasn't looking for investors — he wanted a technical co-promoter who understood the LLM tooling space. Priya, who runs EvalKit, saw the listing on a Tuesday afternoon and sent a message within the hour. They spent two weeks on calls, shared cap tables under NDA, and agreed on a 2.5% for 1.8% equity swap structured as a Delaware LLC interest assignment. The paperwork took four days. Both founders say the swap gave them something a cash deal never could: genuine skin in each other's outcomes. Arjun now routes evaluation questions to EvalKit's docs. Priya's onboarding flow links to PromptLayer for teams that want prompt versioning. Neither paid a broker. The signed agreement sits in both their data rooms.

Lena had $4,200 set aside for marketing but no idea where to spend it. She'd tried paid search and gotten nothing. A friend mentioned builderkin. She listed Docsmith AI with a cash-for-promo offer and received three responses in five days. The Compiler Newsletter, a weekly digest for backend engineers with 22,000 subscribers, proposed a three-month dedicated slot plus a co-authored tutorial. The deal was structured as a services agreement with a performance clause: if open rates on Docsmith mentions fell below 28%, Lena could claw back the final month's payment. They signed via DocuSign. Docsmith's trial signups rose 340% in the first month. Lena has since listed a second swap — this time offering equity.