What are some alternatives?
When comparing Syncthing and SpiderOak, you can also consider the following products
Dropbox - Online Sync and File Sharing
Mega - Secure File Storage and collaboration
Box - Box offers secure content management and collaboration for individuals, teams and businesses, enabling secure file sharing and access to your files online.
Google Drive - Access and sync your files anywhere
Nextcloud - With Nextcloud enterprises host their own secure cloud solution for storage, collaboration & communication from any device, anywhere.
Microsoft OneDrive - Secure access, sharing & file storage