I am trying out MoneyDance. I'm a new Linux user, and am trying to ditch Microsoft Money (which I still use on a Parallels virtual machine). Money is excellent, and does everything that I need.
One key item for me for a financial software is envelope budgeting. Of course, MS Money doesn't support it natively, but I have tweaked a simple way to implement it. MS Money supports, in addition to its normal category system, two user-defined category systems. Note: "category systems". By this, I mean that users can create up to two completely distinct hierarchies of accounts. In additional to the traditional default category system, I use one user-defined system to implement my envelope budgeting system, and I use the other to implement MoneyDance-style tags. (While tags are great, they are not as extensive as a full-blown category system.)
For example, perhaps I go to a restaurant with friends. In the traditional category system, this would be under Expenses: Food: Dining Out. Under my user-defined envelope system, I would also categorize this as Personal: Allowance. (That is my $100-a-month envelope with which I can do whatever I like, as distinct from my Living:Groceries envelope). In addition, depending on the case, I might choose to tag the same transaction with the tag "Mike's visit" to track how much I spent when my friend came to town.
At first blush, this might look like something that could be implemented with tags, but it is not. Tags are optional and somewhat arbitrary; my user-defined categories (envelopes in my case) are required for every single transaction. (Required by me, not by MS Money; but I regularly check reports that ensure that every single transaction, or split of a transaction, that is, every single dollar, is assigned an envelope.)
In summary, does MoneyDance have a similar user-defined category system that co-exists alongside the standard category system, but without conflicting with it? Envelopes are a practical application of this system, but no doubt other users would be able to find other uses. If you do add this feature, I would strongly recommend that you permit the user to implement multiple simultaneous systems, if they so choose, rather than limiting it to just two, as in MS Money.
If my description of this system is not clear, then I'll be glad to further explain it in follow-up postings. Of course, you might need to actually look at MS Money to fully understand it. I don't know if Quicken has this feature; one of the reasons that I have never used Quicken is that I could not find such a feature when I looked (but perhaps it exists under another name).