I have used Lucidchart to make flow charts of work processes. This helps you think the process through as well as give you sharable documentation. I have also used it to layout a web page idea to share with others and to show to the website designer. Because of how easy it is to move elements around, it would be very useful to use for Site Analysis or Schematic Design bubble diagrams when you are just trying to get relationships worked out.
There is a free version that allows 60 elements per chart. I have exceeded this limit a few times and then realized that I didn't need all the elements that I had. So generally the limit for the free version is not a handicap. The paid versions are not very expensive when paid annually: Basic - $3.33/mo for 100 Mb storage, Pro - $8.33/mo for 1 Gb storage, and Team - $21/mo for 5 Gb. See the subscription levels and features.
Even if you don't use the free Google Chrome for your browser, it is worth getting it just for Lucidchart. To get Lucidchart go to the Google Web Store from a blank tab or window, search for Lucidchart, sign up so you can save your work, and you are ready to roll.