These are some of my favorites:

EspoCRM: EspoCRM is an open-source web application that allows you to manage contacts, leads, and opportunities. It's relatively lightweight and can be run on a local server. You can add notes, set reminders, and it has a user-friendly interface.

SuiteCRM: A fork of SugarCRM's Community Edition, SuiteCRM is a fully-featured CRM system that can handle contacts, notes, and reminders. It can be customized to be lighter weight depending on your needs. It's suitable for local deployment.

Vtiger Open Source: Vtiger's open-source version is another option for contact management. It includes the ability to manage contacts, set reminders, and add notes. It's web-based, and you can run it locally.

YetiForce: YetiForce is designed to be a robust open-source CRM system. Although it includes many features, you can customize it to keep only what you need, making it as lightweight as you like.

Fat Free CRM: This is a Ruby on Rails-based CRM that is designed to be simple and lightweight. It offers basic CRM functionalities including contact management, notes, and reminders.