Question: I'm looking for a tool that can help me create remixes and mashups with ease, is there something that can adjust key and tempo for me?

If you want a tool to make remixes and mashups, Fadr is a good option. This web-based service has a collection of AI-based music tools, including a remix maker, mashup maker and a DJ controller. It also has a key/tempo/chords detector that lets you change tempo and key for a smooth transition. Fadr offers a free version, Fadr Basic, and a paid version, Fadr Plus, with more advanced options like the ability to separate individual drum and melody stems.

Another option is Samplab, an AI-based polyphonic audio sample editing tool. You can automatically change tempo and key to smoothly blend samples, which is great for remixes and mashups. Samplab also can edit polyphonic audio and offers a free version with limited features and a paid version with more advanced abilities.

If you need to manipulate audio more broadly, Moises has a variety of AI-based tools. It includes a smart metronome, real-time chord detection and AI key detection, which makes it good for musicians who want to practice at their own tempo and in any key. Moises works on multiple devices for greater flexibility and convenience.

Last, Cryo Mix has a collection of AI-based mixing and mastering tools. Although geared more toward improving audio quality, it includes stem separation and pitch correction tools that can be useful for remixes and mashups. The service is designed to make high-quality audio production accessible to people of all skill levels.