Soulver can automatically insert thousands separators for you so that 1000000 becomes 1,000,000. This feature must be manually enabled in the
Editing preference pane because it can cause issues when working with years (hopefully we'll solve these issues and be able to enable it by default).
Hold down shift and hover over a number to show the scrubber. Drag left or right to play with the number.
You can actually use Soulver to evaluate text anywhere in macOS via services. Simply highlight some text anywhere, right click and choose Services > Calculate with Soulver. There are three services: one calculates and copies the result to the clipboard, one replaces the input with the result, and one appends the result.