Site: https://www.gitkraken.com/
Git Kraken is a heavily advertised Git GUI. It is a free application for open source projects and $50/year for an individual license. Prior to finding Git Kraken, I used Atlassian SourceTree, which is also on this list and is free. I found that GitKraken has an easier to use interface for almost all basic Git tasks. Atlassian has a better code diff tool and is able to perform more complex operations, which Git Kraken has some difficulty with.
Site: https://www.grammarly.com/
This is a tool that can analyze your writing, for grammar and spelling, on web or office documents. I found this program extremely useful during my Masters program; however, I can’t justify paying the subscription fee when writing is not my day job.
Site: https://www.litmus.com/
This is a service that allows for mass testing of emails across multiple devices/operating systems at once. Great for testing responsive emails and if you receive user feedback from a user with a particular type of device. Unfortunately, this is not a cheap service, and is likely best left to businesses.