Fox' dev instance - GoToSocial

GoToSocial does not provide its own webclient, but implements the Mastodon client API. You can use this server through a variety of other clients:

Pinafore

Pinafore is a web client designed for speed and simplicity.

Tusky is a lightweight mobile client for Android.

Get Tusky

Or try one of the clients listed on the official Mastodon page.