I've been working since the GenCon announcement to create a set of BattleScribe catalogues for Star Wars: Legion. I'm excited to have a working army builder for this game, even if it is a little bare-bones at this point. I'll continue updating it as more spoilers happen and more products are announced.
In case you don't know, BattleScribe is a generic army building program that can be used with just about any miniatures war game. The program itself can be found at https://www.battlescribe.net (for Windows or Mac) with mobile versions on Google Play (for Android) or the iOS App Store. It's free (though you can pay a small amount for a premium version) and it doesn't require you to be online to build or access your army lists (though you do need to periodically connect to update your game data as more content is added).
On its own, BattleScribe doesn't do anything. You need to download catalogues for each game you play. Catalogues for most miniature war games are available here (http://battlescribedata.appspot.com/) and are also free. The catalogues on that website are maintained by a passionate fan community. As part of that community, I solely maintain the files for X-Wing, contribute on the files for Star Wars: Armada, and now I built the Star Wars: Legion files from scratch. The Legion file specifically is here: http://battlescribedata.appspot.com/repos/star-wars-legion/index.bsi
BattleScribe has been part of the 40K community for a very long time, and if you play multiple miniatures games, it's a great way to keep your army lists all in the same program and format. Don't worry if you're new to BattleScribe; it's pretty easy to figure out.
As to the Legion files specifically, I believe I have every spoiled Unit Card, Upgrade Card, and Command Card in place and ready to go, with the exception of the AT-RT Flamethrower (which I really can't implement without knowing the cost).
The force organization chart is in place, as well as the rules for choosing a hand of Command Cards as explained by Alex Davy in the Team Covenant demo video (though it's a little uninteresting now with only one Commander per side). Your roster will have a little flag saying it is illegal until you add at least one Commander, three Corps, and a hand of Command Cards.
When you view your roster, the program will modify each unit's stat line as appropriate. For instance, the number of models in the Stormtrooper stat line will increase if you buy the upgrade that adds an extra Stormtrooper. Rebel Troopers will gain the Precise 1 keyword if they buy the Targeting Scopes upgrade (while Stormtroopers would have their Precise 1 keyword upgraded to Precise 2 if they bought Targeting Scopes).
For this game, I find that the roster is easier to read if you set your Roster View with "Inline profiles" and "Inline rules and summary" but it's up to you. There's lots of ways to read it, so play around with what you think works best for you. From Roster View, you can also export your final army list in a variety of formats (PDF, html, as a BattleScribe file to be edited on another device, etc).
There are a few little quirks based on the pre-release nature of this. First and foremost is that we don't know the official names for all the icon types. For instance, Luke has three upgrade slots available. Two are for Force powers, but I don't know if that icon is called "Force" or "Force power" or something else. His third icon might be "Equipment", "Gear", or whatever other name. I just made some assumptions and I'll adjust them when we get an official answer. As far as I know, nobody has any idea what the yellow cog-shaped icon is on the vehicle cards, so I just guessed and put in a place-filler name until we know better. The other quirk is that everything is subject to change until we get an official release, so don't get too attached to anything because it could still change.
In any event, I hope this is useful to people. I'll keep updating and maintaining as more content is revealed or as people point out errors. If you've got questions or if you find errors, please let me know and I'll correct them. I don't have anything to do with the development of BattleScribe itself, so if you have some sort of technical problem or issue with the program itself, I probably can't help (not that I expect you would). However, if the game information is wrong (incorrect point costs or abilities, typos, etc) or the army list isn't validating correctly (like giving you an illegal list flag when your list is legal), I can probably fix that.
Have fun!