SigPen is flat-rate e-signature software that lets businesses send unlimited documents for legally binding electronic signatures — with no per-envelope fees. Unlike DocuSign and other usage-based tools, SigPen charges a simple monthly flat rate starting at $9/month, making it ideal for teams that send documents regularly. Key features include unlimited document sending, AI-powered form field detection, reusable signing links, customizable templates, full audit trails, bulk sending, and API access. SigPen is built for real estate agents, HR teams, legal professionals, and any business that needs a reliable, affordable way to collect signatures at scale.