Ramón Soto Mathiesen
Sign Sign (sign2x). Multi-sign documents locally (privacy) relying on mathematics for security and correctness
Have you ever tried to sign a document for your bank based on the proprietary solution provided by NemID + e-Boks? Or have you tried one of the many other closed and proprietary solution (and wannabe monopolistic): Visma Addo, Penneo, DocuSign, ...? 
If yes, you will find out that most of these solutions are based on you uploading your documents to their servers, both for signing as well for validating. Already based on the approach that you will have to submit confidential documents to some third party should turn on the red light but, what if any of these companies goes into bankruptcy, what will happen to your valid "signed documents"? 
What if I told you that you soon will be able to download a GPL-3.0 SPA (Single Page Application) from a website (https://sign2x.org, please mirror when online) and locally sign your documents or validate without anybody else having to know about it? 
To achieve this, the SPA relies on well known cryptographic approach which is recognized and accepted worldwide (RSA which is used to handle, among others, safe bank transaction) and the core library on which it's built-on that is used by the most widely-used cryptographic e-mail provider in the world (OpenPGP.js).
An extra feature of the upcoming SPA is that it provides a feature that allows to multi-sign documents with an extra bit of mathematics (𝑞 : ℕ<0XA061 → ℤ*<0XA061, 𝑞(𝑥) = 0X9D97 + 0X16A0𝑥 + 0X300A𝑥2) to ensure that some,any,all of the signers comply with the requirements of the document.
Bio
Ramón Soto Mathiesen is a passionate computer scientist, with flair for business, that advocates for correctness, code-quality and high-standards but always with the customer in focus. 
He has been around for a while and have tried almost every position there is in IT. Starting as an IT-supporter back in 2000, to a System Administrator, a Web Developer, a Kernel Developer, a Consultant, a Software Architect, a CTO of a department and at the moment, a founder of an IT company. 
While in these positions, he has done a variety of task related to network, infrastructure, software development, consulting, teaching, technical leadership and probably the most important of them all: inspiring. 
Ramón has been delivering Open Source software since 2006-08-18, as you can see from the first post on his blog, and has been a member of the Free Software Foundation for almost 10 years (November 2007).