Without further ado, here's my list .... I'll keep it updated.
I find Loox easy to set up, support is super helpful, and the widgets look great. They're working hard on integrations so the Loox app can connect to many others and share data. Most importantly, it's effective -- I see my clients get a higher percentage of responses when they switch to this app, particularly if they also add a Messenger or SMS integration.
I've seen abandoned cart notifications and review requests achieve CLICK rates of 90% or more using messenger marketing. It's fantastic if the messenger demographic fits your audience. Recart is one of my favourite tools for it because it creates many natural "subscribe to messenger" points throughout the customer journey, thereby enabling you to reach a greater number of clients on this channel.
It integrates perfectly with Loox for product reviews.
Manychat has some really create messenger marketing and chatbot features, but, I find it doesn't embed as deeply into Shopify as Recart does. However, where Manychat really shines is in the area of "personal shoppers" ... complex question/answer hierarchies that can be set up to help a customer arrive at the best product for them. Recart has some basic functionality in this area, or, to go really elaborate it integrates with Manychat to knock the feature out of the park.
The decision to try to upsell/cross-sell customers is a tricky one. On one hand, you want to get the highest possible margin per order ... on the other hand, you don't want to clutter up your website with offers, or, create too many pop-up interruptions on the customer's journey to check out. That's where ReConvert comes in -- you can offer upsells and cross sells AFTER the order is complete, on the Thank you page! You can make them time sensitive with countdowns and they can be tailored and customized based on the products in the customer's order. Love it.
Much as I'd prefer not to think about it, stuff goes wrong. Sites get hacked or mistakes get made and data gets lost or corrupted. I've heard enough horror stories that I always recommend Rewind -- this app is basically like a time machine for your store that makes it easy to go back to various points in the past. A wonderful "undo" button. You can roll back your entire shop, areas of your shop, or individual things like singular products. Its fantastic, it has a free plan for startups, and I'm recommending it despite it having no affiliate link for me to share :)