It's a hard problem because the top list of websites is so personal... And what you have to lose is in no way proportional to the site's popularity on any index of popular sites.
And only you know where you might have accounts.
For instance, I consider gaming sites to be more critical than banking sites. Because there are much fewer controls and less legal peril involved in hacking MMO gaming accounts, so they are the darlings of crackers. On the other hand, if you're done with Maplestory, you may not care.
But you certainly don't need to care about your Eve Online account if you definitely never played it. Only you know this sort of thing.
If you think you might have used a site in the past, why not just try your old credential?
Why not just spam every website with password reset requests?
They're not going to cooperate with large scale automated requests of this type.
First, the website acknowledging whether an email has an account, would empower spear phishing. Scammer gets a billion emails (easy enough), they start banging the website's password reset to learn "does this email have an account here, or not?" Now they have a list of 1 million emails that do. Now they start spear-phishing those known account holders. Put them on a daily newsletter where unsubscribe requires a login, that kind of thing. This is a "many email addresses against a single site" attack. The site's best defense is to add friction to the password reset process, e.g. a CAPTCHA, or simply design the password-reset process so it tells the inquirer nothing about whether an account exists. This is even more important for sites like Ashley Madison or Furries where having an account there could be embarrassing.
Second, if a cracker managed to gain control of an email, they could simply do exactly what you're trying to do - ascertain which websites this email has an account on. With a full dossier, they can then attack those sites or simply sell the credentials for more than they could otherwise. This is a "single email vs many sites" attack. In this case, the site needs to control one-off access to the password reset function - something like a CAPTCHA is called for. And 2-factor authentication - but again, this 2FA must not disclose to the casual inquirer whether an account here exists.
Because of this, I don't see a probability of anyone writing an app to do this. The writer would find herself in a hacking "arms race" with many companies trying to stop her automation from working.