These builds are updated nighly with the latest improvements to Mudlet and give you a chance to play around with and give your feedback on upcoming features in the next update.
If you're a script author, or just a regular player, it also gives you a chance to help test the next version of Mudlet to ensure regressions don't happen! While we test every improvement that comes to Mudlet, having more eyes on quality will naturally increase the net that finds any bugs trying to sneak in.
If you're already running a PTB version, big thank you! There's a special icon to enjoy: