Back in February, Google's VP of Communications, Nick Fox, revealed that the desktop client for Allo would arrive soon. In May, he gave a specific time frame, saying that Google Allo for desktop is just "a month or two from public release." Fast forward to July, and there is no Google Allo available for desktop yet. Fortunately, it looks like this client is still in the cards.
Amit Fulay, Google Allo's Head of Product, answered a question regarding the web version of this instant messaging app on Twitter by saying "On it ... few more weeks" and nothing more. If the delay is similar to the one faced by Google Drive's transition to Backup and Sync, the launch should happen this summer.
We also have no idea if the web client will be the only way to use Google Allo on desktop devices or at least one dedicated app will be released. We would like to see at least a Windows and a macOS variant coming out, but nothing is certain at this stage.