DocsTeach is a favorite resource of mine for U.S. History teachers and students. I used it and it's predecessor fairly regularly when I was teaching U.S. History. DocsTeach provides an online space where you can create primary source based lessons for your students to complete online or offline. Last fall I published a detailed tutorial on how to create lessons with it. If you'd like some live instruction on how to use it, DocsTeach is hosting a series of free webinars in August.
On August 4th, 6th, 11th, and 13th at 2pm ET DocsTeach staff will host 20 minute webinars about how to use the features of DocsTeach for online instruction. Advanced registration is required in order to participate in the live webinars. Register here.