A new Windows 10 for PCs Insider Preview build is available in the Fast ring, which is 15058. There are no new features in the build, as there haven't been any for the past few weeks.
This is because we're now getting really close to the Creators Update, which is slated to arrive for everyone in April. Microsoft, however, is rumored to be working on signing off on the RTM this week, so we may see the final build as early as next week.
Because of this, you can also expect to see builds more frequently than the usual one per week. In fact, this one replaces 15055 in the Fast ring, which was offered to Insiders just four days ago. Indeed, this period is all about working on fixes for known issues.
While we haven't installed the new build just yet, @tfwboredom on Twitter says that the watermark and expiration date are gone in this build, which is something that happened already in 15042, and was added back later. This is yet another sign that we're getting close to a finalized build.
From here on in, everything should move pretty quickly. Once the RTM build is out, it will be moved to the Slow ring, ISOs will be published, and it will eventually be promoted to Release Preview.