Like having a Mathematica Lite

Very easy to pick up, especially useful for small tasks where Mathematica feels like overkill and takes too much to set up. Far superior to clicking buttons on a virtual calculator on your screen. Documents easily serve as guides for setting up spreadsheets, or larger Mathematica documents, or to simply share the work with coworkers or professors. Even if they don’t have Soulver, its Send to Mail feature generates a correctly formatted, editable table in the mail message that preserves line numbers, values and results.

The only reason I don’t give all five stars*: ratios of dimensions can occasionally lead to incorrect results. For example:
(20 g/L) / (5 g/L) correctly gives 4, but
(20 mg/L - 5 mg/L) / (20 mg / L) gives 750 L/meter^3
Although the answer is technically a correct answer (you can verify this in Wolfram|Alpha), the desired behavior is to instead cancel the units and not perform any scale conversions to fundamental SI units.

However, there is a workaround using the num() function to strip the units:
(num(20 mg/L) - num(5 mg/L))/num(20 mg/L) correctly gives 0.75
So, just be aware that this can happen, and know when to use the workaround.

*The developer is aware of the issue and is investigating.

Sceadugenga about Soulver 2