The adjective experimental is good for describing things that are still in a trial stage. An experimental drug is usually tested in a lab for years before being used on patients.
Something that's experimental is at an early stage, being observed, tested out, and subjected to experiments as it's being developed. An experimental space craft might be launched and watched from afar as scientists decide what changes to make before it can be used for human space exploration. Experimental medicines are sometimes tested on animals before they're given to people. The 15th century meaning was "having experience," from the Latin root experimentum, "test or trial."