Can I deduct the cost of online management applications (e.g., CRM, document e-signing app, QB, etc.) If so, does it matter which category I list them under in TT?

You cannot deduct these on your personal deductions, but if you have a business you can.

You could include it under Office Supplies, or if you wanted more detail you could list them under Miscellaneous Expenses.

Thank you.  I do have a business. 

I agree with @JohnB5677 , so if  you have filed a Schedule C then you can deduct those expense(s) for that business. 

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What Is a Schedule C IRS form? - TurboTax Tax Tips & Videos