Welcome to Flash Apps by Fluorescent (Formerly Obsidian)

Build a cart that converts

★★★★★ 4.7 rating

Extend the functionality of your cart to supercharge your sales. Add handpicked or global cross-sells, customizable cart blocks, and conversion-optimized features to boost sales.

Build a custom slide-out cart with module app blocks.

✓ Easily arrange cart blocks with Theme Editor's drag-and-drop feature.

✓ Arrange in the layout that fits your store’s needs.

✓ Select from available app blocks or embed new app blocks.

Boost conversions with in-cart handpicked or global cross-sells.

✓ Add highly relevant hand-picked suggestions or leverage Shopify's recommendation algorithm for automatic recommendations.

✓ A sleek and mobile-friendly variant selector when users add recommended items to their cart.

✓ Add cross-sells in the Added-to-Cart Popup.

Add conversion-optimized features to your checkout experience

✓ Boost conversions with a Free Shipping Countdown Bar based on your shipping threshold.

✓ Enhance cart with sleek low inventory labels.

✓ Build trust with Payment icon block.

✓ Promote sales, discounts, and links with an eye-catching announcement banner.

✓ Set clear expectations by adding shipping, return, and exchange notes.


Supports multi-currency and multi-language


Features detailed reporting & insights


Increase AOV with hand-picked cross-sells


Use the product page example below to add a product to your cart and see Flash Cart in action.

“This is huge! The most sleek upsell app I've seen in the app store. Very easy to install, took about 3 minutes, and it looks amazing. Works seamlessly with our custom theme. Hopefully there will be some more customization options in the future, such as disabling animations and changing font sizes. Amazing work!”

– Scent Circle

“LOVE LOVE LOVE this app so much!!! It is so user friendly, blends seamlessly with our theme, and it looks very sleek. Couldn't be more pleased”

– LIV & Company

“The app was good... but after the new update it became AMAZING! This is on the must-have-list for your store!”

– Morfars

Start cross-selling for free, pick a plan later

Flash Cart is free for your first $250 of cross-selling

Growth plan - Free 14 Day Trial


Unlimited cross-sells

✓ All features

✓ Advanced analytics

✓ Mobile-first design

✓ Quick & easy setup

✓ Streamlined, beautiful experience

Plus Plan - Free 14 Day trial


Unlimited cross-sells

✓ All features

✓ Advanced analytics

✓ Mobile-first design

✓ Quick & easy setup

✓ Streamlined, beautiful experience

✓ Early access to new features

Fits seamlessly with

Working seamlessly
with Fluorescent Themes

Flash Apps is part of Fluorescent Design — we build beautifully-designed themes with a high-level of customizability, allowing merchants and agencies to create highly-curated, and unique experiences.

We build our apps to fit and work perfectly with Fluorescent Themes — curating highly performing stores, that are optimized for conversion through the whole user flow from homepage to checkout.

We're here to help.

We've got you, promise.

Backed by an outstanding Canadian support team.

The cliches are true: we're friendly and apologize for no reason. Our support team is standing by Monday to Friday, 10am to 6pm PST, to help you get the most out of our apps.