I think I'm going to try to gather similar appearing Chinese characters (including all radicals) here to help one study Chinese contrastively. Characters may be placed in multiple sections; though redundant, this should help with comprehensiveness (and some redundancy is good for helping learning anyways).
Cut and paste these into Annotator to catch multiple characters meanings at once (say to contrast those in a given section).
There can even be mnemonics added for a given grouping.
The purpose of such a system, even though there is no inherent or even likely meaningful, etymological, or phonetic relationship between the groupings, is for learners of Chinese to be able to know the meaning and distinctions between all of the variants of a similar shape, so that when encountering a character, these groupings could be called to mind. Otherwise, the Chinese learner must be repeatedly confused when finding out that there is another character similar to the one he or she thought she had correctly identified. And, as with all comprehensive approaches, it should build a sense of confidence and progress that one has mastered a clear (if small) segment of the total body of characters.
Even though they are arranged here in groupings which may be more readily identified by those familiar with Roman alphabets, these groupings should mostly be nonarbitrary and the patterns discernable (although other groupings may not be created because they would not be familiar to those familiar with a Roman alphabet). For example, the following characters may have similar top portions, but because they do not fit our typical way of grouping items, they are not put into a common category (though they could be): 丷 㐅 . Besides, the use of Roman alphabetic groupings should further assist those with such familiarity. (I am stating all of this because this system could be adopted for those familiar with other scripts, or even for Chinese learners (adult or children) whether just starting out with literacy or brushing up on and refining their productive (or even receptive) capacities.)
There may also be intended (or unnoticed) multiple constrastive patterns within a group (not spelled out here) which may be further discerned by the student (Generally speaking, the characters most similar according to the category at hand are grouped on the same line or immediately below).
There will of course be some correlation with stroke number (whether the actual way Chinese are accustomed to write or merely in appearance (i.e., some characters that are supposed to be written in two strokes could be written in one, etc.)), but shape is the more overarching principle here, so these cannot be strictly divided by stroke number (well, they could be, but there would be some loss of comprehensiveness in listing confusables).
2/Z or S-shaped (or question mark):
Vertical (including with wings):
T with curve (right to left down)
Lower case T with curve:
(Upside down or sideways) V (or Y)-shapes: (order below is rotating V clockwise)
U or upside-down U-shapes:
Multiple U's (also forks or E's)
P-shapes (lower-case e):
C-shape (with or without an extra prong in the middle (or edge))
(Finished with Stroke 2 and radicals stroke 2)
3 strokes to finish (some already above):
㐃, 㐄, 㐇, 㐈, 㐉, 㔾, 㔿, 万, 丈, 上, 下, 丌, 个, 丫, 丸, 久, 乆, 乇, 么, 义, 乊, 乞, 也, 习, 乡, 亇, 亍, 于, 亏, 亐, 亡, 亼, 亽, 亾, 亿, 兀, 兦, 凡, 凢, 凣, 刃, 刄, 劜, 勺, 卂, 千, 卄, 卪, 卫, 叉, 夨, 子, 孑, 孒, 孓, 宀, 寸, 小, 尢, , 巾, 干, 幺, 广, 弋,弓, 忄, 扌, 才, 氵, 犭, 纟, 门, 阝, 飞, 饣, 马, 兀