If you just want a simple and effective live chat widget, then it's a hassle to install and manage a fully integrated customer service platform just to get live chat.
If you already use Slack, then Acorn Chat is a great simple solution for you, but if you don't use Slack, then here is a list of standalone live customer chat widgets that I'd recommended checking out:
Crisp is a fully featured live chat widget including mobile apps, triggers and canned responses. It also has a knowledge base and integration with Facebook messenger and twitter DMs, which is a nice addition if you hare managing your social accounts as well.
They are reasonably priced (per inbox instead of per agent, and have all the features a small business would need from a live chat solution.
If you grow (or are a large company), you may want more features that only come in some of the larger customer service platforms
LiveChat is part of a larger suite of tools, but since they are all priced individually, you can easily just sign up for the LiveChat widget. It has Facebook messenger integration, a lot of analytics and reporting, and even has mobile app integration if you have a mobile app.
LiveChat has a large customer base and a great feature set, and is backed by a larger company (so they aren't going anywhere anytime soon)
It's priced per agent, per month, so the costs will start to go up as your team size increases or if you want to buy into the rest of their software packages.
Olark is one of the larger competitors (in terms of size and feature set) in the live chat space. They can handle larger companies with team management, and have some nice features like live chat translation and a wide variety of integrations.
They have a live chat focus and have the feature set to support both small and large customers.
Their pricing goes up to $59 per seat per month to remove the Olark branding, which may be too much for small businesses just looking to quickly try out live chat.
PureChat is a standalone live chat app with native iOS and Android apps. They have a focus on user analytics and contact info so that you can track your visitor's information.
They have mobile apps if you're on the go, and also have integrations for a variety of other software solutions
They are not as established as some of the other competitors on this list, and their price point seems a bit high for a standalone live chat solution.
If you need more than just a standalone live chat app, then there are several good choices that are fully integrated customer service platforms.
Or, if you want to use a simple live chat widget that sends messages to Slack (instead of having "yet another app" open all the time), then check out Acorn Chat, which is a reasonably priced alternative to some of the larger, more complex live chat software packages.