Token Allowance Checker shows all approvals for your ERC20-compliant tokens, and the option to change the approved amount - or completely zero it.
Many DApps have the habit of requiring you to approve effectively unlimited amount of tokens. This helps improving the user experience, as you only have to sign off an approval once and it will be enough for all future transactions.
However this also means that the DApp (or the person/entity controlling it) can at any time transfer all of your tokens, without requiring any further approval.
In addition, there is no concept of expiring approvals. Once approved, the approval will remain forever. If you do not trust a DApp or its operators anymore, there is usually no easy way to remove the approval.
Since the dfuse.io backend service is not available anymore, Token Allowance Checker remains offline for now.
I'm working on a replacement service to retrieve allowances but it is unclear when this will be available.