Catalyst Game Labs have released two novels and a PDF based supplement for BattleTech.
From their website:
Era Digest: Age of War is now available for sale. We also released two novels as epub/mobi files – Assumption of Risk and Binding Force. You can grab those at the BattleShop, DTRPG or the Kindle store (when it updates, the Kindle store can be up to a week to propagate through Amazon’s system.)