Filestash has the plug built in.

Filestash puts a web interface in front of whatever storage you already have — S3, SFTP, WebDAV, a plain directory — and it carries a WOPI editor plugin in its core. Point that plugin at SumOffice and the files open in our engine. No patching, no fork.

What was measured

The round	`.xlsx` and `.docx` opened from the Filestash interface, edited, saved back. `.xlsm` opened through the WOPI window — see the limitation below.
What came back	VBA byte for byte, all five pictures byte for byte, the edit in place.
The one thing to know	Filestash has no file locking. The editor works without it, which means two people opening the same file are not held apart by the storage — if that matters for your team, a host with locks (Nextcloud, Infinite Scale, SharePoint) is the safer seat.
Limitation, on the Filestash side	`.xlsm` is not in its own list of editable types, so the macro workbook opens through the WOPI window rather than a click in the file list.
What this does not say	The round used a fixture workbook from our corpus that asks Microsoft Excel to repair it on its own, before any round. So no silent-Excel claim here; that claim lives on Nextcloud and Seafile, where we measured it on a real workbook.

Setting it up

# the editors, behind your TLS address
git clone https://github.com/SumOfficeApp/sumoffice-docker && cd sumoffice-docker/nextcloud
cp env.example .env    # PUBLIC_URL=https://office.example.com
docker compose up -d

# Filestash → admin console → the WOPI editor plugin
# discovery URL:  https://office.example.com/hosting/discovery

Evaluation is free with no time limit; production is the per-application license. The other systems we measured →

Then

Check my Excel file — what your workbooks rely on, in seconds.
Tell us what you run behind Filestash — the storage decides how versions behave.