Drupal Forge is offered as a community service. The 6-hour temporary disposable Drupal sites, with or without Dev environments are completely free.

Drupal Forge spins up pre-configured sites for you. Each site configuration is called a template. You provide some basic information and Drupal Forge sends you a link when your site is ready.

Drupal Forge is built on DevPanel. 

However, Drupal Forge uses a very limited version of DevPanel with only its basic features.

You can check out DevPanel's website to learn more about it if you like.

You can't really compare Tugboat to Drupal Forge (DF). It's like comparing Apples to Oranges. 

SimplyTest.me is a service built on Tugboat. Drupal Forge is a service built on DevPanel.

If you want to compare Tugboat to something, you can compare it to DevPanel. 

GitPod is awesome. Drupal Forge (DF) is very similar to it in many ways. Here are the similarities and differences:

Simplytest is a great service. We were in fact inspired by it. If you have not tried it, you should try it out. Seriously. Here's the link. Drupal Forge is a community service - just like Simplytest. Here are the similarities and differences: