In the late 1990's and early 2000's I founded a company called 24Link which initially produced a personal webserver which allowed users to host content directly from their Window's PC onto the Internet. At its peak there were over 50,000 users of the service with thousands of users logged in at any one time. Both the desktop server and the remote server components were written in C.
After working with an incubator and securing angel investment the company pivoted to a peer-to-peer file sharing application remarkably like Dropbox (which appeared 5 years later). Unlike Dropbox we were limited to peer-to-peer communication and storage since we did not have access to a scalable storage engine like Amazon S3.
The pivoted to product was not able to secure follow on funding during the following dotcom "bust" and the business was closed.