I use Fossil-SCM for that. 100% OSS, it's a single Sqlite DB file for backups, etc. It's totally fine being offline or online and totally fine being de-synchronized for years and catching up.

I put my legal and financial info on a USB stick with the fossil binaries every year, and hand them out to next of kin. Whenever I die they just plug in the USB and click the appropriate fossil binary and bam, they get everything with a web interface, files and wiki with instructions included.