What's the simplest electronic signature solution available?

The simplest e-signature solution is usually a PDF you sign with a built-in signature tool, such as:

• Adobe Acrobat / Acrobat Reader
• Preview on Mac
• Microsoft Edge / built-in PDF viewer in some cases

If you mean the simplest service for sending and collecting signatures, a common easy option is:

• Dropbox Sign (HelloSign) or DocuSign for basic workflows

If you want the absolute simplest approach for a one-off signature:

1. Open the document as a PDF
2. Use the app’s Sign or Draw signature tool
3. Insert your signature
4. Save and send

If you want, I can recommend the simplest option based on your exact need:

• signing your own document
• getting someone else to sign
• legal/business use
• free vs paid