**Reason**
Unmaintained, @Legoktm said in https://gerrit.wikimedia.org/r/c/mediawiki/extensions/GoogleAppEngine/+/460740/ that this extension should be archived.
**To-do list**
- This task
-- [x] Add maintainers of that extension/skin as subscribers to this task (if they have no apparent Phabricator account, notify them on-wiki or via email if possible and note it here).
-- [x] Add Phabricator project #mediawiki-extensions-googleappengine as a tag for this task, and remove #mediawiki-extensions-other/#other-skins as appropriate.
- On-wiki documentation
-- [x] Archive documentation on `mediawiki.org` (https://www.mediawiki.org/wiki/Extension:GoogleAppEngine): replace page contents with `{{Archived extension|last revision id before archiving|task=T######}}`; replace `T######` with this task's number.
-- [x] If documentation page was translatable, remove `<translate>`, visit Special:PageTranslation, and click "remove from translation" (if you don't have the translation administrator right, ask a [[ https://www.mediawiki.org/wiki/Special:ListUsers/translationadmin | user who does ]]).
-- [x] Update Wikidata item (https://www.wikidata.org/wiki/Special:EntityPage/Q21677343) associated with documentation page
--- [x] add statement `Abandonware (Q281039)` to `instance of (P31)` together with qualifier `start time (P580)` = the YYYY-MM-DD date that you decided to archive extension/skin (generally per edit history)
--- [x] add qualifier `end time (P582)` = the YYYY-MM-DD (same date as above) to `instance of (P31) = MediaWiki extension (Q6805426)/MediaWiki skin (Q21996535)`
- Phabricator
-- [x] Mark all Phabricator tasks for the extension/skin either Declined or Invalid. Add a comment pointing to this task when doing so for reference.
-- [x] Archive Phabricator project #mediawiki-extensions-googleappengine for the extension/skin.
-- [x] Edit Phabricator project #mediawiki-extensions-googleappengine description for the extension/skin with a link to this ticket.
- Translatewiki.net/translations
-- [ ] Remove from `translatewiki.net` ([[ https://gerrit.wikimedia.org/r/plugins/gitiles/translatewiki/+/refs/heads/master/groups/MediaWiki/mediawiki-extensions.txt | groups/MediaWiki/mediawiki-extensions.txt ]] / [[ https://gerrit.wikimedia.org/r/plugins/gitiles/translatewiki/+/refs/heads/master/groups/MediaWiki/mediawiki-skins.txt | groups/MediaWiki/mediawiki-skins.txt ]]).
- Configuration/tests/integrations/etc.
-- [x] Remove tests in [[ https://gerrit.wikimedia.org/g/integration/config | integration/config ]] ([[ https://gerrit.wikimedia.org/r/plugins/gitiles/integration/config/+/master/zuul/layout.yaml | zuul/layout.yaml ]]).
-- [x] ~~Remove manifest/other references from [[ https://gerrit.wikimedia.org/r/plugins/gitiles/mediawiki/vagrant/+/master | mediawiki/vagrant ]] if they exist.~~
-- [x] ~~Remove from https://doc.wikimedia.org/cover-extensions/ if present (requires #continuous-integration-infrastructure shell user to delete directly from the server).~~
- Repositories
-- [x] Empty repository, leaving only the README indicating the repo is archived, and referring to this task by URL.
-- [ ] Remove from [[ https://gerrit.wikimedia.org/r/plugins/gitiles/mediawiki/extensions/+/master | mediawiki/extensions ]] / [[ https://gerrit.wikimedia.org/r/plugins/gitiles/mediawiki/skins/+/master | mediawiki/skins ]] (along with in `.gitmodules`).
-- [x] Mark the repository read-only in Gerrit (also edit description to prepend "[ARCHIVED]" and a reference to this task): (https://gerrit.wikimedia.org/r/admin/repos/mediawiki/extensions/GoogleAppEngine).
-- [x] Archive the Diffusion repository for the extension/skin: ({rEGAE}).
-- [x] Delete the GitHub mirror: (https://github.com/wikimedia/mediawiki-extensions-GoogleAppEngine).