There are a number of apps that do this but if you just want an online web-version, Play Store has you covered. This direct link will direct you to Google's own Apps on Sale page where it shows limited time free and paid apps.
And the link for the whole page of Pre-Registration Games (be alerted once they go live) is here.
I figured i'd post this since I hadn't seen it before nor anyone posted it that I had noticed, either.
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Not that I know of, nor does the Notification section is of much help either. To receive updates you can use optionally AppSales, PAGF or the likes. FreeAppsNow tends to have more free limited apps/games than AppSales, in comparison but no apps/games on sale, from what I can see.
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