Christian Rassin

Perfect for adding tips, charity donations or optional contributions directly in the WooCommerce cart.
Cart Donation for WooCommerce allows customers to easily add a donation directly from the cart page.
The plugin automatically creates a hidden donation product and adds it to the cart using a smooth AJAX experience.
This plugin does not collect or store personal data on its own.
Requires WooCommerce to be installed and activated.
Perfect for:
<ul>
<li>Charity donations</li>
<li>Tips</li>
<li>Support contributions</li>
<li>Rounding up orders</li>
</ul>
<h3>Features</h3>
<ul>
<li>Custom donation amounts</li>
<li>Quick-select donation buttons</li>
<li>AJAX add-to-cart (no page reload required)</li>
<li>Only one donation item in cart (automatically replaced)</li>
<li>Fully removable donation item</li>
<li>Multi-language support (EN, NL, FR, DE, ES, IT)</li>
<li>Customizable donation box title</li>
<li>Custom donation product image</li>
<li>Lightweight and fast</li>
<li>Compatible with most properly coded WooCommerce themes</li>
</ul>
<h3>Usage</h3>
<ul>
<li>Customers can enter a custom amount or use quick-select buttons.</li>
<li>Only one donation is active in the cart at a time.</li>
<li>Adding a new donation replaces the previous one.</li>
<li>Donations are added via AJAX for a smooth experience.</li>
</ul>
Note: 
The donation option in the cart is only displayed when another product has been added. You can then remove that product, leaving only the donation in the cart.
Pro version: Create and place multiple donation blocks in the cart or anywhere on your website using flexible placement options, shortcode support, and many more advanced features.

Cart Donation for WooCommerce

Easily add donations or tips to your WooCommerce cart with custom amounts, quick buttons and a smooth AJAX experience.

phonebook

This plugin inserts a TipMe icon in WordPress posts if the user has a Twitter username and has put the Twitter link in their website field of their profile. 
TipMe buttons for BBPress posts are inserted so users can get tips if they just have a 
Twitter link defined in the website field of their profile.
In short, it creates a tweet that the ChangeTip bot pics up and delivers with just one click.
We are using it on some of our web sites, so thought others might enjoy using it on theirs, but it comes without any warranty express or implied, and should be used at your own risk. It is a quite simple concept so should be quite reliable.
This probably will work with earlier versions of WordPress, but has not been tested.

TipMeWP

Inserts a "Tip Me" icon in WordPress & BBPress posts if user has a Twitter account & has put the Twitter link in website field

Cart Donation for WooCommerce vs TipMeWP