Q: What exactly is the HotA build?
A: This is too complicated to answer without a post of its own. (See below) I also highly suggest watching some or all of the videos linked to, especially if you'd rather skip reading the details.
Q: I'm a DTWW barb, can I use HotA?
A: Chances are you can get by fine with your current build and gear. There are several variations of WW/HotA hybrid builds which work very effectively. The simplest way to work it in is to replace either war cry or OP:KS with it, and leave a fury generator. Simply use HotA against rare elites, goblins, and pesky kiting elites and leave your playstyle unchanged otherwise. If you're accustomed to running without a fury generator, you can use hybrids using OP:KS or Rend which are covered in the following post.
Q: What type of gear works best with HotA? Do I have to use a Skorn?
A: Being able to stand in the thick of things and HotA mobs down without the movement that's typical of DTWW requires high defenses. Stack resistances and HP as heavily as you can within your budget. It will give you much more build flexibility. As far as weapons go, HotA alternates damage between the mainhand and offhand, so low-DPS stat sticks that are typical for DTWW are undesirable. The higher the damage of both of your weapons, the better. Skorn is a popular choice because it gives you tremendous damage without having to worry about balancing damage ranges. It is by no means necessary. Dual-wield setups can be at least as powerful if done correctly. Critical hit chance is especially important, and to a higher degree than it is with DTWW. Critical hit damage is also very important as a properly built HotA barb will be landing crits close to 100% of the time.
Some posts on dual wield versus Skorn later in the thread:
Q: How much HotA resource cost reduction do I need, if any?
A: The answer to this depends heavily on the build you choose. The consensus amongst most experienced HotA barbs is that none is necessary if you use a build that incorporates a fury generator such as bash or frenzy, and plenty argue that reduction makes keeping WotB harder. On the same token, if you want to use a build without a fury generator, such as a WW/HotA hybrid, I would recommend a cost reduction of 4, and 5 on high budgets. Going past 5 is not something I would recommend. You will not be dumping fury quickly enough to permawrath without lots of battle rage spamming, and the other problem is that the gear required is both very rare and usually ends up compromising your gearset heavily. (skull grasp, mara's kaleidoscope, HotA reduction Skorn). The most desirable slot to get it is on a Stone of Jordan.
A thread discussing it:
KillerElite goes into further depth 2 posts below.
Q: If I get a -5 SoJ, can I permanently spam HotA on a single target?
A: No. Of all the runes, HotA:Smash has the highest proc coefficient at 80%, and that means that 20% of your crits won't return any fury through into the fray. Even if you have enough +fury and cc to have a 100% crit chance with a full fury globe, and you have -5 reduction, your fury will strictly speaking, degenerate on a single target given no other sources of fury. In reality, you don't encounter this situation often in farming, but in ubers, a generator is still necessary. In farming, it's common to use a ww/hota hybrid to generate fury from sprint tornadoes and whirlwinding. Just be aware that a -5 SoJ on its own is not going to turn HotA into a pure generator. Going past -5 can allow nearly endless spamming, but makes perma wrath close to impossible and requires heavy gearing tradeoffs as noted above.
Q: Does HotA have breakpoints?
A: Yes, see below. In general, they match up fairly closely with sprint/ww ones, and there are more available. Try to make sure that you are not barely below one when buffed with WotB. Other than that, don't stress over them too much.
Q: I want to use a DTWW/HotA hybrid with my Skorn. How much attack speed do I need?
A: Most of us advocate reaching the 17 tick breakpoint, which requires 1.67 APS when buffed with Wrath of the Berserker. With a non-IAS Skorn, this requires 42% IAS from gear. Nubtro suggests 43% in case you drop wrath of the berserker, as there is a breakpoint at 1.43 APS. With an 11% IAS Skorn, only 26% IAS from gear is necessary to reach the same breakpoint. The 18 tick breakpoint is significantly smoother. This requires 1.82 APS buffed, but it's recommended to also hit the 1.83 APS breakpoint for HotA if you're going this route. With a non-IAS Skorn, this requires 58% IAS from gear, or 7 slots. Don't attempt this without a very large budget. With an 11% IAS Skorn, this breakpoint requires 40% IAS from gear.
Q: Which rune of HotA should I use?
A: The most popular option is Smash due to its high proc coefficient and damage output. It synergizes well for dual wield barbs who use DTWW for their AoE damage. When relying on HotA for AoE damage, other runes can be preferable, as Smash reduces its effective area. Thunderstrike is my favorite, as it stuns mobs easily and consequently makes fury generation easy. Rolling thunder has a low proc coefficient, but has the highest area of effect. All 3 of these runes are worth consideration if you wish for HotA to be your primary source of damage.
Rolling Thunder: .40
The Devil's Anvil: .08
Note: as of now it isn't fully established how the animation lengths work with dual wielded weapons of different speeds. The table below assumes a single weapon or equal speeds for both. Big thanks to Nubtro.