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Actually, the things that have been implemented since it was created over 3 years ago are arguably the following:
It's now been a little over 5 years since the launch of the modern Quicken Mac, and the development team has added a lot of key functionality to the program. Since Quicken became independent of Intuit three-and-a-half years ago, the size of the Mac development team has supposedly doubled. But it's still a fairly small team, and they had to initially spend time re-writing back-end code just to move off some of Intuit's servers; combined with the complexity of the Quicken code and data structures, the progress has been steady but slower than user (or management) had hoped.
Where we stand today is leaps and bounds better than where we started in fall 2014, but there are still important features from Quicken 2007 (and Quicken Windows) which don't yet exist in Quicken Mac. How important these omissions are varies from one user to the next. There are plenty of Quicken Mac users who are happy because the program meets their needs. There are some Quicken Mac users who are wishing for features but find the current program good enough to get along. And there are a smaller number of Quicken Mac users who feel they cannot use Quicken 2020 because of a missing feature they depend on. Only you can determine whether Quicken 2020 meets your needs completely, adequately, or not at all. (Buying and trying Quicken is my advice; if you determine there's a showstopper issue for you, you can get a full refund within 30 days.)
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There are dozens, if not hundreds, of posts on this site about differences between Quicken 2007 and Quicken Mac 2020, and if would be impossible to summarize every detail here. (And if you were to read them all, it will likely scare the %^&*# out of you and you won't give it a shot!)
There are some things that are different and are (at least arguably) better; there are some things that are different that are (arguably) worse; and there are some things you just can't do in Quicken 2020 yet -- although new enhancements appear roughly every other month, so the gap is continually narrowing.
Categories and sub-categories carry over. Classes are converted to tags; tags are arguably better, because you can have more than one tag on a transaction, which wasn't possible with classes; however, Quicken 2007 allowed sub-classes, where tags are all independent and not hierarchical. Existing reports don't carry over at all. The structure of the database and the reports is different enough that they never built a way to convert reports. So if you have a lot of reports, you'll spend some time re-building them. You still can't do all the reports you could in Quicken 2007, but they've been pretty steadily chipping away in this area and the reports are good enough for most users now.
Functions not available? It's hard to quantify, and depends how you define things. QuickMath is an example of a function that is simply not available. (I'm still hoping we'll see that in a future update, but it hasn't been as high a priority for the developers compared to some of the big-ticket functionality like loans and budgeting and flexible reports that they've worked on in recent years.) QuickReports is an example something that doesn't exist in the way it did in Quicken 2007, but there are ways to search/report most data in different ways.Actually, the things that have been implemented since it was created over 3 years ago are arguably the following: