Condless

WooCommerce plugin that sets default attribute for variable products automatically if only 1 option is in-stock.
<a href="https://en.condless.com/default-attributes-for-woocommerce/" rel="nofollow ugc">Documentation</a> | <a href="https://en.condless.com/contact/" rel="nofollow ugc">Contact</a>
Variable product of T-shirt with color attribute (White/Blue/Black) and size attribute (S/M/XL): 
If only Black T-shirts are in-stock: default color (Black), default size (none). 
If only Small T-shirts are in-stock: default color (none), default size (Small). 
If only White and XL T-shirts are in-stock: default color (White), default size (XL).
<h4>How It Works</h4>
<ol>
<li>Before product variations is displayed to the customer, the plugin will check each attribute, and if there is only 1 in-stock option it will be set as the default.</li>
</ol>
<h4>Features</h4>
<ul>
<li>Stock: Set option as default when it’s the only 1 in-stock.</li>
<li>Per Attribute: Set specific option as default in all products with that attribute (from the Edit Attribute screen)</li>
<li>Top: Set as default the first option of each attribute.</li>
<li>Out of stock: Disable out of stock variations.</li>
<li>Add to Cart button: In archive pages display for variable products the attribute name instead of: “Select options”.</li>
<li>Select options: In single product pages remove the select options text if default attribute is set.</li>
</ul>

Default Attributes for WooCommerce

WooCommerce plugin that sets default attribute for variable products automatically if only 1 option is in-stock.

GauravNagpal

Less sold products with special attributes and tags can be sold easily using this feature without affecting sales for popular products. WooCommerce coupon section extension for adding coupons for special attributes and tags.
After enabling this plugin, you will see a new multiple select box in the coupon “User Restriction” section. All the other preferences will not be affected; it will work perfectly as it was before.
<ul>
<li>Work for both attributes and tags</li>
<li>Coupon categories</li>
<li>No new section for coupons</li>
<li>All other existing features will remain the same</li>
<li>Can be clubbed with other WooCommerce coupon rules</li>
<li>Can be applied percentage or a flat amount on products</li>
<li>Supported variable and simple product types </li>
<li>Attribute created in “Products > Attributes” tab are supported</li>
</ul>
If you like this easy plugin and if the plugin is improving your sales, then <a href="https://www.paypal.me/gauravnagpal" rel="nofollow ugc">Donate</a> a little to this development time or at least spend a couple of minutes for feedback.

Attributes Coupon for WooCommerce

WooCommerce coupon section extension for adding coupons for special attributes and tags. Also, you can categorise the coupons.

Default Attributes for WooCommerce vs Attributes Coupon for WooCommerce