The word "Lightning" is used in many context within Salesforce.
It looks like #3 has happened. Salesforce has released two beautiful new tools. Lightning for Outlook and Lightning for Gmail. Both are plugins that you can install today if you are a customer of Salesforce. We believe these plugins are different than the old plugins that were related to RelateIQ.
No, if you are still using classic mode, lightning for outlook and gmail should still work.
Lightning for Outlook is the newer and better version. If you install it, it will automatically disable the old Salesforce for Outlook plugin. See here:https://help.salesforce.com/articleView?id=outlookcrm_sfo_n_ec_limits.htm&language=en_US&type=0
Salesforce has a great matrix here that talks about the various email integration tools:https://help.salesforce.com/articleView?id=sfo_vs_email_connect.htm&language=en_US&type=0
Yes! Opensense signatures will work with all of them. Email templates can also be configured with the Opensense signature.
Opensense email tracking will also seamlessly work with all the tools, so you get the best of all worlds -- Super simple Salesforce related workflows, and our powerful multi-recipient email tracking.
Yes! We are in the final stages of approval with the AppExchange. We will make an announcement when it's officially listed.