Imagine if the HTC EVO 3D's keyboard had a baby with the HTC EVO 4G's keyboard. Then, you taught this baby a bunch of other languages, how to auto-correct (and auto-complete) words, and gave it a handwriting mode.
Well, you don't have to imagine it anymore because it actually exists and can supposedly be installed on any HTC EVO 3D with Sense 3.0 – rooted or unrooted, deodexed or odexed (YMMV however).
EVO 3D user michaelm_007 has gone through the dirty work of porting this keyboard to the phone, and it looks to be about 98% complete and fully functional for daily use. There have already been seven releases for it, a good sign that he's continually trying to hammer out the bugs and keep his users happy.
Along with the super awesome trace mode (that comes stock with the EVO 3D), this keyboard includes the old school arrows. This is a welcome edition to some, and dreaded by others (see the comments below).
There is a flashable .zip for root users, but I would probably just recommend using this .apk, which again should be compatible with rooted and non-rooted EVO 3Ds. Note that if you are using an odexed ROM (like myn's Warm TwoPointThree), you should rename or delete your HTC_IME.odex in your /system/app folder just to be safe.
After the installation, head over to Settings > Language & keyboard > Touch Input and check out all the options. This is where you can switch to a ton of different languages and enable the trace mode.[xda-developers]
Thanks to all the commenters that pointed out that trace comes stock with the EVO 3D… I feel silly for not noticing that… Whoops!