Quillstack

Quillstack sells a hosted payments core aimed at early-stage fintechs that want to own their product logic without writing a ledger from scratch. Accounts, holds, transfers and fee schedules are declared as configuration, and a full-fidelity sandbox simulates returns, chargebacks, partial captures and rail outages on demand.

Teams use the simulator to write contract tests against edge cases that are hard to reproduce in production, such as an ACH return arriving after the funds were already paid out, before a sponsor bank reviews the program.