user1580: What wallets currently support RBF? 
Is there some workaround if they don't?

user14871: As far as I know other than bitcoin core API's (as renlord suggested) the only wallet that conveniently supports the functionality is GreenAddress

user19338: As I answered in another question, Electrum Bitcoin Wallet has the feature. I've confirmed that mac client worked. It seems that Android app has the same feature.
https://electrum.org/#download
Which clients offer a way to replace unconfirmed transactions?

user31586: No wallet currently supports creating replaceable transactions conveniently. To work around this, you can manually create raw transactions from scratch.
The following are suggested instructions for use with bitcoin-cli.
To create a replaceable transaction. You can use "createrawtransaction" to manually add inputs and mark the "nsequence" field to a value less than 0xffffffff. If you would like to replace the first transaction created this way. You will have to dump the transaction to free the UTXOs for use again using the "abandontransaction" command. 
Once you've dumped the first transaction. You should be able to repeat the process above then increment the "nsequence" field. This new transaction when broadcasted should then be accepted by any node that supports full RBF. 

1580: <p>What wallets currently support RBF? 
Is there some workaround if they don't?</p>
 14871: <p>As far as I know other than bitcoin core API's (as renlord <a href="https://bitcoin.stackexchange.com/a/44524/14871">suggested</a>) the only wallet that conveniently supports the functionality is <a href="https://bitcoinmagazine.com/articles/greenaddress-is-first-bitcoin-wallet-to-launch-replace-by-fee-bitcoin-transactions-miner-adoption-slow-1463516896" rel="nofollow noreferrer">GreenAddress</a></p>
 19338: <p>As I answered in another question, Electrum Bitcoin Wallet has the feature. I've confirmed that mac client worked. It seems that Android app has the same feature.</p>

<p><a href="https://electrum.org/#download" rel="nofollow noreferrer">https://electrum.org/#download</a></p>

<p><a href="https://bitcoin.stackexchange.com/questions/22699/which-clients-offer-a-way-to-replace-unconfirmed-transactions/52932#52932">Which clients offer a way to replace unconfirmed transactions?</a></p>
 31586: <p>No wallet currently supports creating replaceable transactions conveniently. To work around this, you can manually create raw transactions from scratch.</p>

<p>The following are suggested instructions for use with bitcoin-cli.</p>

<p>To create a replaceable transaction. You can use "createrawtransaction" to manually add inputs and mark the "nsequence" field to a value less than 0xffffffff. If you would like to replace the first transaction created this way. You will have to dump the transaction to free the UTXOs for use again using the "abandontransaction" command. </p>

<p>Once you've dumped the first transaction. You should be able to repeat the process above then increment the "nsequence" field. This new transaction when broadcasted should then be accepted by any node that supports full RBF. </p>
