I am using my Lowe's card for a 6 month 0% financing offer. Can I still use my card for purchases and receive the normal grace period or does interest start on purchases instantly?
You can still keep using the card as normal. Your promotional purchases are held in a separate bucket (and shown in their own tab online). Unless the promotional balance is not paid prior to expiration (after which, retroactive interest is applied and the usual grace period rules apply) as long as your monthly payments satisfy the minimum amounts to cover all new charges in addition to the minimum payment amount that would be applied to your promotional balance, you are fine. One caveat is that Synchrony will usually apply payments in the last month or two of a promotional balance differently; there should be a selection tool if you want to override their default, but the default would apply payment to the promotional balance(s) before new purchases in the final days of that promo (if it satisfies the remaining balance, this is actually much better for the cardholder - if it doesn't, it likely makes no difference).
Thanks so much!
@K-in-Boston Home Depot does the same for the last few months I just wanted to add this DP as I was recently told this but they told me to be sure if I have it signed up to take it off a few months before the end of the Promotion because they will automatically add it in that way they can be sure the payments go straight to promotion in the final months and he also mentioned to me to be sure to CALL it when looking to pay it off to make sure they can be sure to apply it properly to the Promotional Items FIRST! I didn't know about that so it's Neat that Lowe's is similar in that aspect!
Can you have multiple financing promotions simultaneously?
@Poppa For HD or Lowes I know for HD you can since I have the HD card! 
I had 3- 1 that was 6 month and 2 that were 24 month ones at the same time at one point (the 6 month is off and I'm almost done with my 24 month ones now)
@Poppa wrote:Can you have multiple financing promotions simultaneously?
Yes. If they are deferred interest promos and not equal payment promos, payments are applied to the balance(s) that have the earliest expiration.