The list of Summer ’17 below only apply to Salesforce Classic.
There are additional Summer ’17 features available to Lightning Experience only and to both Lightning and Salesforce Classic. Visit the Summer ’17 Release Highlights post.
1.Lightning Experience Migration Assistant. Who can miss this section in Classic setup?
The assistant tool provides links to “Learn” about LEX, “Check Readiness”, “Preview”, “Optimize with Features”, “Set Up Users” and “Turn It On.” In the “Set Up Users” section, you can specify which users you are going to switch to LEX.
Check Readiness delivers a report in a few minutes to your inbox. The report will go through various sections and provide an assessment. Here is an example of the Lightning Readiness Report for the related lists in my org.
2. Update existing Letterhead email templates by changing which letterhead is associated with the template.
3. Control the Order and Order Product fields that appear on a Visualforce page with field sets.
4. Cloud Scheduler retirement: Unavailable in Salesforce orgs created in Winter ‘17 or later. If you enabled Cloud Scheduler before Winter ‘17, it remains available until Winter ’18.
5. Stay-in-Touch feature officially retires. The Request Update button will be removed in Summer 17.
Jenwlee's Salesforce Blog 
Thanks so much for doing this, Jen. I always find something useful from your insights and the way you split up your posts is helpful for us SF Classic diehards.
LikeLike
Thank you. I’m happy you find them to be helpful.
LikeLike
Always come back to your website for a quick cross-reference. Thanks for doing this, Jen!
Do you mind sharing what software tool you use in your blogs for screenshots (like GIFs)?
LikeLike
You’re welcome. The tool is called ScreentoGIF.
LikeLike
Thanks a lot, Jen! Appreciate that.
LikeLike
There are other free software to record, edit and convert to gif. I switched to another tool this weekend because mouse movements were not very responsive in screentogif.
LikeLike