The web wallet masternode landed on a fork during the wee hours and has since been corrected for now.
It reminds a lot of NXT - is HEAT built on top of their codebase?
Yes originally based on NXT yet heavily modified since 2014. Still uses NXT p2p layers and cryptography.
I would like a README-user.md somewhere
The current versions have been put out in rush to fix early network malfunctions. Proper readme will hopefully follow with the next release.
Can I use just ANY SecretPhrase?
Yes. Use a sufficient number of random characters or at least 10 words.
Is it wise to show the SecretPhrase as cleartext in your input field?
No

Sign in unfortunately is preliminary still aimed for stakeholders mostly
Is the "Load BTC" functionality working?
Yes. Manual monitoring and verifications during the early phases of the network may take a bit longer than 1 confirmation for Load, and about 24 hours for withdrawals.
the account balances in the heatwallet.com are wrong since some A2A trades. when do we get a full account based transaction history to have a proof?
Please supply more information which account and which balance is wrong, it would help us in tuning things. PM or email to support at heatledger dot com works also if you mind sharing that publicly. Thanks.