Alternativ till SlideMail för Ruby med kommersiell licens

• Ruby
  Alla plattformar Windows Mac Linux Chrome OS Android iPhone Apple Watch Android Wear iPad Android Tablet Windows S Web Self-Hosted BSD Haiku PortableApps.com Slack F-Droid Chrome Ruby Gmail Cloudron Amazon Echo (Alexa Voice Service) PureOS (Purism)
• Kommersiell licens
  Eventuell licens Gratis licens Open Source-licens Kommersiell licens