Today's #FreeSoftwareAdvent is paperless-ngx, a key part of keeping us, well, paperless.
It is a document management tool, but I use it in a very basic way: it is hooked up to our scanner, and anything we scan gets automatically converted to PDF and OCRd. We then shred the paper. I try to scan, and shred, everything on the day that it arrives.
It is particularly useful around tax return time, as it means I can easily get the information I need from stuff which people have posted to us.