具有免费许可证的Haiku版SlideMail的替代品

• Haiku
  所有平台 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)
• 免费许可证
  任何牌照 免费许可证 开源许可证 商业牌照