Elrails has been merged into mainline, and can be found in the nightlies.
Electric rails adds a fourth rail-type to the game, enabling the realistic addition of electric engines, which, well, need elrails to operate.

OpenTTD 0.4.7 is a hotfix for the previous release. In this a nasty bug has crept, due to improper testing, that prevented the pathfinder (NPF) to work correctly. This greatly set back the gaming-experience so it was decided to do another release than to have you suffer from this.
"You can safely upgrade from 0.4.5 to this version as hopefully nothing has gotten broken, only fixed." <- I can confirm this though making it valid for 0.4.7.

As usual, you can find the release on SourceForge. There is also a forum post to spill your feelings, and a scenario package that you might want to use with the source files.

• Downloads
• TT-Forums post

OpenTTD is back with a quick release. This time no new features only bugfixes. But at least this one is hot on the heels of 0.4.5 and should work more pleasantly. You can safely upgrade from 0.4.5 to this version as hopefully nothing has gotten broken, only fixed. Have fun.

As usual, you can find the release on SourceForge. The files are in the process of being uploaded and distributed so have a little patience when some releases are not found on SF.

• Downloads
• TT-Forums post

Currently, we are in the process of making electric rail available in OpenTTD! Because this involves a lot of big changes, we are creating it outside of the main development. Therefore, it isn't included in the nightlies. But, no need to be sad, you can download the latest version of elrail here:

Warning: using 'elrail' can unrecoverable damage your savegame, which can't be loaded by any version of OpenTTD. Do not report bugs related to this. You have been warned!

Electric Rail - Binaries

If you find problems in it, please don't report them via the webpage, but send a mail to {mailto:celestar@openttd.org} or post them at the forum-topic. Please read the BUGS file before doing so.

Also, don't be shy to tell Celestar what a great job he did!

A long time in the making, more than 8 months, OpenTTD 0.4.5 has finally been released. Improved multi-player, newgrf, autoreplace and countless other fixes/features have been added. Also the downloads are quite bigger than the last one as you can see because we have included 16 scenarios with the release; a result of a semi-contest on the forums. We hope you enjoy them.

As usual, you can find the release on SourceForge.

• Downloads
• TT-Forums post